| **Summary of Significant Accounting Policies** | 12 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          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| **Accounting Policies [Abstract]**             |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   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| Summary of Significant Accounting Policies     | Summary of Significant Accounting PoliciesBasis of PresentationThe Consolidated Financial Statements include the accounts of CNA Financial Corporation (CNAF) and its subsidiaries.  Collectively, CNAF and its subsidiaries are referred to as CNA or the Company.  Loews Corporation (Loews) owned approximately 89.6% of the outstanding common stock of CNAF as of December 31, 2021.The accompanying Consolidated Financial Statements have been prepared in conformity with accounting principles generally accepted in the United States of America (GAAP).  Intercompany amounts have been eliminated.  The preparation of Consolidated Financial Statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the Consolidated Financial Statements and the reported amounts of revenues and expenses during the reporting period.  Actual results may differ from those estimates.Recently Adopted Accounting Standards Updates (ASU) ASU 2016-13: In June 2016 the Financial Accounting Standards Board (FASB) issued ASU No. 2016-13, Financial Instruments-Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments.  The updated accounting guidance required changes to the recognition of credit losses on financial instruments not accounted for at fair value through the Company’s results of operations.  For financial assets measured at cost, the expected credit loss model requires immediate recognition of estimated credit losses over the life of the asset and presentation of the asset at the net amount expected to be collected.  This updated guidance applies to mortgage loan investments, reinsurance and insurance receivables and other financing receivables.  For available-for-sale fixed maturity securities carried at fair value, estimated credit losses will continue to be measured at the present value of expected cash flows, however, the other than temporary impairment (OTTI) concept has been eliminated.  Under the previous guidance, estimated credit impairments resulted in a write-down of amortized cost.  Under the updated guidance, estimated credit losses are recognized through an allowance and reversals of the allowance are permitted if the estimate of credit losses declines.  For available-for-sale fixed maturity securities where the Company has an intent to sell, impairment will continue to result in a write-down of amortized cost.On January 1, 2020, the Company adopted the updated guidance using a modified retrospective method with a cumulative effect adjustment recorded to beginning Retained earnings.  Prior period amounts have not been adjusted and continue to be reported in accordance with the previous accounting guidance.  A prospective transition approach is required for available-for-sale fixed maturity securities that were purchased with credit deterioration (PCD assets) or have recognized an OTTI write-down prior to the effective date.  The cumulative effect of the accounting change resulted in a $5 million decrease in Retained earnings, with a corresponding $7 million allowance for credit losses recorded for Mortgage loans partially offset by a $2 million tax impact.The allowance for uncollectible reinsurance and insurance receivables was unchanged as a result of adopting the updated guidance.  At adoption, an allowance for credit losses of $6 million was established for available-for-sale fixed maturity securities that were PCD assets, with a corresponding increase to amortized cost, resulting in no adjustment to the carrying value of the securities. See the accounting policy discussion within this Note, as well as Notes B and G to the Consolidated Financial Statements for additional information regarding credit losses.Accounting Standards Pending AdoptionIn August 2018, the FASB issued ASU 2018-12, Financial Services-Insurance (Topic 944): Targeted Improvements to the Accounting for Long-Duration Contracts.  The updated accounting guidance requires changes to the measurement and disclosure of long-duration contracts. Entities will be required to update cash flow assumptions (including morbidity and persistency) at least annually, and to update discount rate assumptions quarterly using an upper-medium grade fixed-income instrument yield.  The effect of changes in cash flow assumptions will be recorded in the Company's results of operations and the effect of changes in discount rate assumptions will be recorded in Other comprehensive income.  The guidance is effective for interim and annual periods beginning after December 15, 2022, with early adoption permitted, and may be applied using either a modified retrospective transition method or a full retrospective transition method. Restatement of prior periods presented is required. The Company will adopt the new guidance effective January 1, 2023, using the modified retrospective method applied as of the transition date of January 1, 2021.  The most significant impact at the transition date will be the effect of updating the discount rate assumption to reflect an upper-medium grade fixed-income instrument yield, which will be partially offset by the de-recognition of shadow adjustments associated with long duration contracts.  The Company expects the net impact of these changes will be a material decrease in Accumulated other comprehensive income as of the transition date.  The requirement to update cash flow assumptions at least annually is expected to change the pattern of earnings emergence being recognized.  Adoption will also significantly expand the Company’s disclosures, and will impact systems, processes, and controls.  While the requirements of the new guidance represent a material change from existing GAAP, the new guidance will not impact capital and surplus under statutory accounting practices, related cash flows, or the underlying economics of the business.The Company continues to make progress in connection with these matters and is in process of refining key accounting policy decisions, technology solutions and updates to internal controls associated with adoption of the new guidance.  These in-progress activities include modifications of actuarial valuation systems, data sourcing, analytical procedures and reporting processes.  Insurance OperationsPremiums: Insurance premiums on property and casualty insurance contracts are recognized in proportion to the underlying risk insured and are principally earned ratably over the term of the policies.  Premiums on long term care contracts are earned ratably over the policy year in which they are due.  The reserve for unearned premiums represents the portion of premiums written relating to the unexpired terms of coverage.Property and casualty contracts that are retrospectively rated or subject to audit premiums contain provisions that result in an adjustment to the initial policy premium depending on the contract provisions.  These provisions stipulate the adjustment due to loss experience of the insured during the coverage period, or changes in the level of exposure to insurance risk.  For such contracts, the Company estimates the amount of ultimate premiums that the Company may earn upon completion of the coverage period and recognizes either an asset or a liability for the difference between the initial policy premium and the estimated ultimate premium.  The Company either adjusts such estimated ultimate premium amounts during the course of the coverage period based on actual results to date, or by conducting premium audits after the policy has expired to determine the final exposure to insured risks.  The resulting adjustment is recorded as either a reduction of or an increase to the earned premiums for the period.Insurance receivables include balances due currently or in the future, including amounts due from insureds related to paid losses under high deductible policies, and are presented at unpaid balances, net of an allowance for uncollectible receivables.  A loss rate methodology is used to determine expected credit losses for premium receivables.  This methodology uses the Company’s historical annual credit losses relative to gross premium written to develop a range of credit loss rates for each dollar of gross written premium underwritten.  Additionally, an expected credit loss for amounts due from insureds under high deductible and retrospectively rated policies is calculated on a pool basis, informed by historical default rate data obtained from major rating agencies.  Changes in the allowance are presented as a component of Other operating expenses on the Consolidated Statements of Operations.  Amounts are considered past due based on policy payment terms.    Insurance receivables and any related allowance are written off after collection efforts are exhausted or a negotiated settlement is reached.  See the Credit Losses section of this note for additional information on the Company’s allowances for expected credit losses.Claim and claim adjustment expense reserves: Claim and claim adjustment expense reserves, except reserves for structured settlements not associated with asbestos and environmental pollution (A&EP), workers' compensation lifetime claims and long term care claims, are not discounted and are based on i) case basis estimates for losses reported on direct business, adjusted in the aggregate for ultimate loss expectations; ii) estimates of incurred but not reported (IBNR) losses; iii) estimates of losses on assumed reinsurance; iv) estimates of future expenses to be incurred in the settlement of claims; v) estimates of salvage and subrogation recoveries and vi) estimates of amounts due from insureds related to losses under high deductible policies.  Management considers current conditions and trends as well as past Company and industry experience in establishing these estimates.  The effects of inflation, which can be significant, are implicitly considered in the reserving process and are part of the recorded reserve balance.  Ceded claim and claim adjustment expense reserves are reported as a component of Reinsurance receivables on the Consolidated Balance Sheets.  Claim and claim adjustment expense reserves are presented net of anticipated amounts due from insureds related to losses under deductible policies of $1.1 billion and $1.2 billion as of December 31, 2021 and 2020.  A significant portion of these amounts are supported by collateral.  The Company has an allowance for uncollectible deductible amounts, which is presented as a component of the allowance for doubtful accounts included in Insurance receivables on the Consolidated Balance Sheets.Structured settlements have been negotiated for certain property and casualty insurance claims.  Structured settlements are agreements to provide fixed periodic payments to claimants.  The Company's obligations for structured settlements not funded by annuities are included in claim and claim adjustment expense reserves and are discounted at a weighted average interest rate of 6.4% and 6.5% as of December 31, 2021 and 2020.  As of December 31, 2021 and 2020, the discounted reserves for unfunded structured settlements were $503 million and $520 million, net of discount of $621 million and $657 million.  For the years ended December 31, 2021, 2020 and 2019, the amount of interest recognized on the discounted reserves of unfunded structured settlements was $36 million, $35 million and $36 million, respectively.  This interest accretion is presented as a component of Insurance claims and policyholders’ benefits on the Consolidated Statements of Operations, but is excluded from the Company’s disclosure of prior year loss reserve development.Workers' compensation lifetime claim reserves are calculated using mortality assumptions determined through statutory regulation and economic factors.  As of December 31, 2021 and 2020, workers' compensation lifetime claim reserves are discounted at a 3.5% interest rate.  As of December 31, 2021 and 2020, the discounted reserves for workers’ compensation lifetime claim reserves were $228 million and $258 million, net of discount of $97 million and $113 million.  For the years ended December 31, 2021, 2020 and 2019, the amount of interest accretion recognized on the discounted reserves of workers’ compensation lifetime claim reserves was $12 million, $15 million and $21 million, respectively.  This interest accretion is presented as a component of Insurance claims and policyholders' benefits on the Consolidated Statements of Operations, but is excluded from the Company's disclosure of prior year loss reserve development. Long term care claim reserves for policyholders that are currently receiving benefits are calculated using mortality and morbidity assumptions based on Company and industry experience.  These long term care claim reserves are discounted at a weighted average interest rate of 5.8% as of December 31, 2021 and 2020.  As of December 31, 2021 and 2020, such discounted reserves totaled $2.7 billion, net of discount of $428 million and $439 million. Future policy benefit reserves: Future policy benefit reserves represent the active life reserves related to the Company's long term care policies for policyholders that are not currently receiving benefits and are computed using the net level premium method, which incorporates actuarial assumptions as to morbidity, persistency, inclusive of mortality, discount rate, future premium rate adjustments and expenses.  Expense assumptions primarily relate to claim adjudication.  These assumptions are locked in over the life of the policy; however if a premium deficiency emerges, the assumptions are unlocked and the future policy benefit reserves are increased.  The September 30, 2021 gross premium valuation (GPV) indicated that recorded reserves included a margin of approximately $72 million.  Long term care active life reserves for policy holders not currently receiving benefits are discounted at a weighted average interest rate of 5.3% and 5.4% as of December 31, 2021 and 2020.In circumstances where the cash flow projections supporting future policy benefit reserves are expected to result in profits being recognized in early future years followed by losses in later future years, the future policy benefit reserves are increased by an amount necessary to offset losses that are projected to be recognized in later future years.  The Company has not recorded additional future policy benefit reserves for profits followed by losses.Insurance-related assessments: Liabilities for insurance-related assessments are accrued when an assessment is probable, when it can be reasonably estimated and when the event obligating the entity to pay an imposed or probable assessment has occurred.  Liabilities for insurance-related assessments are not discounted and are included as part of Other liabilities on the Consolidated Balance Sheets.  As of December 31, 2021 and 2020, the liability balances were $79 million and $82 million.Reinsurance:  Reinsurance accounting allows for contractual cash flows to be reflected as premiums and losses.  To qualify for reinsurance accounting, reinsurance agreements must include risk transfer.  To meet risk transfer requirements, a reinsurance contract must include both insurance risk, consisting of underwriting and timing risk, and a reasonable possibility of a significant loss for the assuming entity.Reinsurance receivables related to paid losses are presented at unpaid balances.  Reinsurance receivables related to unpaid losses are estimated in a manner consistent with claim and claim adjustment expense reserves or future policy benefit reserves.  Reinsurance receivables are reported net of an allowance for uncollectible amounts on the Consolidated Balance Sheets.  The cost of reinsurance is primarily accounted for over the life of the underlying reinsured policies using assumptions consistent with those used to account for the underlying policies or over the reinsurance contract period.  The ceding of insurance does not discharge the primary liability of the Company.The Company has established an allowance for uncollectible reinsurance receivables which relates to both amounts already billed on ceded paid losses as well as ceded reserves that will be billed when losses are paid in the future.  For assessing expected credit losses, the Company separates reinsurance receivables into two pools: voluntary reinsurance receivables and involuntary receivables related to mandatory pools.  The Company has not recorded an allowance for involuntary pools as there is no perceived credit risk. The principal credit quality indicator used in the valuation of the allowance on voluntary reinsurance receivables is the financial strength rating of the reinsurer sourced from major rating agencies. If the reinsurer is unrated, an internal financial strength rating is assigned based on the Company’s historical loss experience and the Company’s assessment of reinsurance counterparty risk profile, which generally corresponds with a B rating.  Reinsurer financial strength ratings are updated and reviewed on an annual basis or sooner if the Company becomes aware of significant changes related to a reinsurer.  The allowance for uncollectible reinsurance receivables is estimated on the basis of periodic evaluations of balances due from reinsurers, reinsurer financial strength rating and solvency, industry experience and current and forecast economic conditions.  Because billed receivables generally approximate 5% or less of total reinsurance receivables, the age of the reinsurance receivables related to paid losses is not a significant input into the allowance analysis.  Changes in the allowance for uncollectible reinsurance receivables are presented as a component of Insurance claims and policyholders' benefits on the Consolidated Statements of Operations.  See the Credit Losses section of this note for additional information on the Company's allowances for expected credit losses.Amounts are considered past due based on the reinsurance contract terms.  Reinsurance receivables related to paid losses and any related allowance are written off after collection efforts have been exhausted or a negotiated settlement is reached with the reinsurer.  Reinsurance receivables from insolvent insurers related to paid losses are written off when the settlement due from the estate can be reasonably estimated.  At the time reinsurance receivables related to paid losses are written off, any required adjustment to reinsurance receivables related to unpaid losses is recorded as a component of Insurance claims and policyholders' benefits on the Consolidated Statements of Operations.A loss portfolio transfer is a retroactive reinsurance contract.  If the cumulative claim and allocated claim adjustment expenses ceded under a loss portfolio transfer exceed the consideration paid, the resulting gain from such excess is deferred and amortized into earnings in future periods in proportion to actual recoveries under the loss portfolio transfer.  In any period in which there is a revised estimate of claim and allocated claim adjustment expenses and the loss portfolio transfer is in a gain position, the deferred gain is recalculated as if the revised estimate was available at the inception date of the loss portfolio transfer and the change in the deferred gain is recognized in earnings.Deferred acquisition costs: Deferrable acquisition costs include commissions, premium taxes and certain underwriting and policy issuance costs which are incremental direct costs of successful contract acquisitions.  Acquisition costs related to property and casualty business are deferred and amortized ratably over the period the related premiums are earned.  Deferred acquisition costs are presented net of ceding commissions and other ceded acquisition costs.The Company evaluates deferred acquisition costs for recoverability.  Anticipated investment income is considered in the determination of the recoverability of deferred acquisition costs.  Adjustments, if necessary, are recorded in current period results of operations.  Policyholder dividends: Policyholder dividends are paid to participating policyholders within the workers' compensation and surety lines of business.  Net written premiums for participating dividend policies were approximately 1% of total net written premiums for each of the years ended December 31, 2021, 2020 and 2019.  Dividends to policyholders are accrued according to the Company's best estimate of the amount to be paid in accordance with contractual provisions and applicable state laws.  Dividends to policyholders are presented as a component of Insurance claims & policyholders' benefits on the Consolidated Statements of Operations and Other liabilities on the Consolidated Balance Sheets.InvestmentsThe Company classifies its fixed maturity securities as either available-for-sale or trading, and as such, they are carried at fair value.  Changes in fair value of trading securities are reported within Net investment income on the Consolidated Statements of Operations.  Changes in fair value related to available-for-sale securities are reported as a component of Other comprehensive income.The cost of fixed maturity securities classified as available-for-sale is adjusted for amortization of premiums and accretion of discounts, which are included in Net investment income on the Consolidated Statements of Operations.  The amortization of premium and accretion of discount for fixed maturity securities takes into consideration call and maturity dates that produce the lowest yield.For asset-backed securities included in fixed maturity securities, the Company recognizes income using an effective yield based on anticipated prepayments and the estimated economic life of the securities.  When estimates of prepayments change, the effective yield is recalculated to reflect actual payments to date and anticipated future payments predominantly using the retrospective method.  To the extent that unrealized gains on fixed maturity securities supporting structured settlements not funded by annuities were realized, or that unrealized gains on fixed maturity securities supporting long term care products would result in a premium deficiency if realized, a related increase in Insurance reserves is recorded, net of tax, as a reduction of net unrealized gains through Other comprehensive income (Shadow Adjustments).  Shadow Adjustments, net of tax, decreased $296 million and increased $575 million for the years ended December 31, 2021 and 2020, respectively.  As of December 31, 2021 and 2020, net unrealized gains on investments included in Accumulated other comprehensive income (AOCI) were correspondingly reduced by Shadow Adjustments of $2,477 million and $2,773 million, respectively.Equity securities are carried at fair value.  The Company's non-redeemable preferred stock contain characteristics of debt securities, are priced similarly to bonds and are held primarily for income generation through periodic dividends.  While recognition of gains and losses on these securities is not discretionary, management does not consider the changes in fair value of non-redeemable preferred stock to be reflective of our primary operations.  As such, the changes in the fair value of these securities are recorded through Net investment gains (losses) on the Consolidated Statements of Operations.  The Company owns certain common stock with the intention of holding the securities primarily for market appreciation and as such, the changes in the fair value of these securities are recorded through Net investment income.  The Company's carrying value of investments in limited partnerships is its share of the net asset value of each partnership, as determined by the general partner.  Certain partnerships for which results are not available on a timely basis are reported on a lag, primarily three months or less.  Changes in net asset values are accounted for under the equity method and recorded within Net investment income on the Consolidated Statements of Operations.  Mortgage loans are commercial in nature, are carried at unpaid principal balance, net of unamortized fees and an allowance for expected credit losses, and are recorded once funded.  The allowance for expected credit losses is developed by assessing the credit quality of pools of mortgage loans in good standing using debt service coverage ratios (DSCR) and loan-to-value ratios (LTV).  The DSCR compares a property’s net operating income to its debt service payments, including principal and interest.  The LTV ratio compares the current unpaid principal balance of the loan to the estimated fair value of the underlying property collateralizing the loan. The pools developed to measure the credit loss allowance use increments of DSCR and LTV to draw distinctions between risk levels. The Company applies expected credit loss rates by pool to the outstanding receivable balances.  Changes in the allowance for mortgage loans are presented as a component of Net investment gains (losses) on the Consolidated Statements of Operations.  Prior to 2020, mortgage loans were evaluated on an individual loan basis considering the collection experience of each loan and other credit quality indicators such as DSCR and the credit-worthiness of the borrower or tenants of credit tenant loan properties.  Mortgage loans were considered to be impaired loans and a loss incurred when it was probable that contractual principal and interest payments would not be collected and any impairment losses were recognized as a direct write-down of amortized cost.  See the Credit Losses section of this note for additional information on the Company’s allowances for expected credit losses.  Interest income from mortgage loans is recognized on an accrual basis using the effective yield method.  Other invested assets include overseas deposits.  Overseas deposits are valued using the net asset value per share (or equivalent) practical expedient.  They are primarily short-term government securities, agency securities and corporate bonds held in trusts that are managed by Lloyd's of London.  These funds are required of Lloyd's syndicates to protect policyholders in overseas markets and may be denominated in local currency.  Short term investments are carried at fair value, with the exception of cash accounts earning interest, which are carried at cost and approximate fair value.  Changes in fair value are reported as a component of Other comprehensive income.Purchases and sales of all securities are recorded on the trade date, except for private placement securities, including bank loan participations, which are recorded once funded.  Net investment gains and losses are determined on the basis of the cost or amortized cost of the specific securities sold.In the normal course of investing activities, the Company enters into relationships with variable interest entities (VIEs), as both an investor in limited partnerships and asset-backed securities issued by third-party VIEs.  The Company is not the primary beneficiary of these VIEs, and therefore does not consolidate them.  The Company determines whether it is the primary beneficiary of a VIE based on a qualitative assessment of the relative power and benefits of the Company and the other participants in the VIE.  The Company’s maximum exposure to loss with respect to these investments is limited to the investment carrying values included in the Company’s Consolidated Balance Sheets and any unfunded commitments.An available-for-sale security is impaired if the fair value of the security is less than its cost adjusted for accretion, amortization and allowance for credit losses.  When a security is impaired, it is evaluated to determine whether the Company intends to sell the security before recovery of amortized cost or whether a credit loss exists.  Losses on securities that the Company intends to sell are recognized as impairment losses within Net investment gains (losses) on the Consolidated Statements of Operations.  If a credit loss exists, an allowance is established and the corresponding amount is recognized as an impairment loss within Net investment gains (losses) on the Consolidated Statements of Operations.  The allowance for credit losses related to available-for-sale fixed maturity securities is the difference between the present value of cash flows expected to be collected and the amortized cost basis, limited by the amount that the fair value is less than the amortized cost basis.  In subsequent periods, the allowance is reviewed, with any changes in the allowance presented as a component of Net investment gains (losses) on the Consolidated Statements of Operations.  Changes in the difference between the amortized cost basis, net of the allowance, and the fair value, are recognized in Other comprehensive income.Significant judgment is required in the determination of whether an impairment loss has occurred for a security.  The Company follows a consistent and systematic process for determining and recording an impairment loss, including the evaluation of securities in an unrealized loss position and securities with an allowance for credit losses on at least a quarterly basis.The Company’s assessment of whether an impairment loss has occurred incorporates both quantitative and qualitative information.  A credit loss exists if the present value of cash flows expected to be collected is less than the amortized cost basis. Significant assumptions enter into these cash flow projections including delinquency rates, probable risk of default, loss severity upon a default, over collateralization and interest coverage triggers and credit support from lower level tranches. The Company considers all available evidence when determining whether an investment requires a credit loss write-down or allowance to be recorded. Examples of such evidence may include the financial condition and near-term and long-term prospects of the issuer, whether the issuer is current with interest and principal payments, credit ratings on the security or changes in ratings over time, general market conditions and industry, sector or other specific factors and whether it is likely that the Company will recover its amortized cost through the collection of cash flows.  See the Credit Losses section of this note for additional information on the Company’s allowances for expected credit losses.Prior to 2020, the Company’s assessment of whether an impairment loss occurred also incorporated both quantitative and qualitative information.Fixed maturity securities in an unrealized loss position that the Company intended to sell, or it more likely than not would be required to sell before recovery of amortized cost, were considered to be impaired and the entire difference between the amortized cost basis and fair value of the security was recognized as an impairment loss in earnings as a direct write-down of amortized cost.The remaining fixed maturity securities in an unrealized loss position were evaluated to determine if a credit loss existed. If a credit loss was determined to exist, the credit loss was recognized in earnings as a direct write-down of amortized cost.Credit LossesThe allowances for credit losses on fixed maturity securities, mortgage loans, reinsurance receivables and insurance receivables are valuation accounts that are reported as a reduction of a financial asset’s cost basis and are measured on a pool basis when similar risk characteristics exist.  Management estimates the allowance using relevant available information from both internal and external sources.  Historical credit loss experience provides the basis for the estimation of expected credit losses and adjustments may be made to reflect current conditions and reasonable and supportable forecasts.  Adjustments to historical loss information are made for any additional factors that come to the Company’s attention.  This could include significant shifts in counterparty financial strength ratings, aging of past due receivables, amounts sent to collection agencies, or other underlying portfolio changes.  Amounts are considered past due when payments have not been received according to contractual terms.  The Company also considers current and forecast economic conditions, using a variety of economic metrics and forecast indices.  The sensitivity of expected credit losses relative to changes to these forecast economic conditions can vary by financial asset class.  The Company considers a reasonable and supportable forecast period to be up to 24 months from the balance sheet date.  After the forecast period, the Company reverts to historical credit experience.  The Company uses collateral arrangements such as letters of credit and amounts held in beneficiary trusts to mitigate credit risk, which are considered in the estimate of net amount expected to be collected.  Amounts are written off against the allowance when determined to be uncollectible.The Company has made a policy election to present accrued interest balances separately from the amortized cost basis of assets and has elected the practical expedient to exclude the accrued interest from the tabular disclosures for mortgage loans and available-for-sale securities.  The Company has elected not to estimate an allowance for credit losses on accrued interest receivable.  The accrual of interest income is discontinued and the asset is placed on nonaccrual status within 90 days of the interest becoming delinquent.  Interest accrued but not received for assets on nonaccrual status is reversed through investment income.  Interest received for assets that are on nonaccrual status is recognized as payment is received.  The asset is returned to accrual status when the principal and interest amounts contractually due are brought current and future payments are expected.  Interest receivable is presented as a component of accrued investment income on the Consolidated Balance Sheet.Prior to 2020, the allowance for uncollectible reinsurance and insurance receivables was measured using an incurred loss methodology. Deferred Non-Insurance Warranty Revenue and Acquisition ExpenseNon-insurance warranty revenue is primarily generated from separately-priced service contracts that provide mechanical breakdown and other coverages to vehicle or consumer goods owners.  The warranty contracts generally provide coverage from 1 month to 10 years.  For warranty products where the Company acts as the principal in the transaction, Non-insurance warranty revenue is reported on a gross basis, with amounts paid by customers reported as Non-insurance warranty revenue and commissions paid to agents reported as Non-insurance warranty expense.Non-insurance warranty revenue is reported net of any premiums related to contractual liability coverage issued by the Company's insurance operations.  Additionally, the Company provides warranty administration services for dealer and manufacturer obligor warranty products, which include limited warranties and guaranteed asset protection waivers.  The Company recognizes Non-insurance warranty revenue over the service period in proportion to the actuarially determined expected claims emergence pattern.  Customers predominantly pay in full at the inception of the warranty contract.  The liability for deferred revenue represents the unearned portion of revenue in advance of the Company's performance.  The deferred revenue balance includes amounts which are refundable on a pro rata basis upon cancellation.Dealers, retailers and agents earn commission for assisting the Company in obtaining non-insurance warranty contracts.  Additionally, the Company utilizes third-parties to perform warranty administrator services for its consumer goods warranties.  These costs, which are deferred and recorded as Deferred non-insurance warranty acquisition expense, are amortized to Non-insurance warranty expense consistent with how the related revenue is recognized.  The Company evaluates deferred costs for recoverability including consideration of anticipated investment income.  Adjustments to deferred costs, if necessary, are recorded in the current period results of operations.Income TaxesThe Company and its eligible subsidiaries (CNA Tax Group) are included in the consolidated federal income tax return of Loews and its eligible subsidiaries.  The Company accounts for income taxes under the asset and liability method.  Under the asset and liability method, deferred income taxes are recognized for temporary differences between the financial statement and tax return bases of assets and liabilities, based on enacted tax rates and other provisions of the tax law.  The effect of a change in tax laws or rates on deferred tax assets and liabilities is recognized in income in the period in which such change is enacted.  Future tax benefits are recognized to the extent that realization of such benefits is more likely than not, and a valuation allowance is established for any portion of a deferred tax asset that management believes will not be realized.  The Company releases tax effects from AOCI utilizing the security-by-security approach for Net unrealized gains (losses) on investments with an allowance for credit losses and Net unrealized gains (losses) on other investments.  For Pension and postretirement benefits, tax effects from AOCI are released at enacted tax rates based on the pre-tax adjustments to pension liabilities or assets recognized within Other comprehensive income.Pension and Postretirement BenefitsThe Company recognizes the overfunded or underfunded status of its defined benefit plans in Other assets or Other liabilities on the Consolidated Balance Sheets.  Changes in funded status related to prior service costs and credits, and actuarial gains and losses arising from differences between actual experience and actuarial assumptions, are recognized in the year in which the changes occur through Other comprehensive income.  Unrecognized actuarial gains and losses in excess of 10% of the greater of the beginning of the year projected benefit obligation or fair value of plan assets (the corridor) are amortized as a component of net periodic pension cost (benefit) over the average remaining life expectancy of the plan participants.  Annual service cost, interest cost, expected return on plan assets, amortization of prior service costs and credits and amortization of actuarial gains and losses are recognized on the Consolidated Statements of Operations.The vested benefit obligation for the CNA Retirement Plan is determined based on eligible compensation and accrued service for previously entitled employees.  Effective June 30, 2015, future benefit accruals under the CNA Retirement Plan were eliminated and the benefit obligations were frozen.Stock-Based CompensationThe Company records compensation expense using the fair value method for all awards it grants, modifies or cancels primarily on a straight-line basis over the requisite service period, generally three years.Foreign CurrencyThe Company's foreign subsidiaries' balance sheet accounts are translated at the exchange rates in effect at each reporting date and income statement accounts are either translated at the exchange rates on the date of the transaction or at average exchange rates.  Foreign currency translation gains and losses are reflected in Stockholders' equity as a component of AOCI.  Foreign currency transaction gains (losses) of less than $(1) million, $13 million and $1 million were included in determining Net income for the years ended December 31, 2021, 2020 and 2019, respectively.LeasesA lease provides the lessee the right to control the use of an identified asset for a period of time in exchange for consideration.  Operating lease right-of-use (ROU) assets and lease liabilities are included in Other assets and Other liabilities on the Company's Consolidated Balance Sheets.ROU assets represent the Company's right to use an underlying asset for the lease term and operating lease liabilities represent the Company's obligation to make lease payments arising from the lease.  The Company determines if an arrangement is a lease at inception.  Operating lease ROU assets and liabilities are recognized at the lease commencement date based on the present value of lease payments over the lease term.  Most operating leases contain renewal options that provide for rent increases based on prevailing market conditions.  Certain leases contain options to terminate before maturity.  The lease term used to calculate the ROU asset includes any renewal options or lease termination options that the Company expects to exercise.  The discount rate used to determine the commencement date present value of lease payments is typically the Company’s secured borrowing rate, as most of the Company’s leases do not provide an implicit rate.  ROU assets include any lease payments required to be made prior to commencement and exclude lease incentives.  The Company has elected to account for its lease and non-lease components as a single lease component.  The Company’s non-lease components consist of variable lease costs not based on an index or rate and are excluded from the measurement of ROU assets and lease liabilities.  Variable lease costs not based on an index or rate are treated as period costs, and represent charges for services provided by the landlord and the Company's reimbursement to the landlord for costs such as real estate taxes and insurance. The Company occupies office facilities under lease agreements that expire at various dates.  The Company's lease agreements do not contain significant residual value guarantees, restrictions or covenants.  The Company does not have any significant finance leases.Property and EquipmentProperty and equipment are carried at cost less accumulated depreciation.  Depreciation is based on the estimated useful lives of the various classes of property and equipment and is determined principally on the straight-line method.  Furniture and fixtures are depreciated over seven years.  Office equipment is depreciated over five years.  The estimated lives for data processing equipment and software generally range from three to five years, but can be as long as ten years.  Leasehold improvements are depreciated over the corresponding lease terms not to exceed the underlying asset life.GoodwillGoodwill represents the excess of purchase price over the fair value of the net assets of acquired entities and businesses.  Goodwill in the International segment may change from period to period as a result of foreign currency translation.  Goodwill is tested for impairment annually or when certain triggering events require such tests. As a result of reviews completed for the year ended December 31, 2021, the Company determined that the estimated fair value of the reporting units were in excess of their carrying value including Goodwill.  Changes in future periods in assumptions about the level of economic capital, business growth, earnings projections or the weighted average cost of capital could result in goodwill impairment.Other Intangible AssetsOther intangible assets are reported within Other assets on the Consolidated Balance Sheets.Finite-lived intangible assets are amortized over their estimated useful lives.  Indefinite-lived other intangible assets are tested for impairment annually or when certain triggering events require such tests.Earnings (Loss) Per Share DataEarnings (loss) per share is based on weighted average number of outstanding common shares.  Basic earnings (loss) per share excludes the impact of dilutive securities and is computed by dividing Net income (loss) by the weighted average number of common shares outstanding for the period.  Diluted earnings (loss) per share reflects the potential dilution that could occur if securities or other contracts to issue common stock were exercised or converted into common stock.For the years ended December 31, 2021, 2020 and 2019, approximately 1 million, 770 thousand and 960 thousand potential shares attributable to exercises or conversions into common stock under stock-based employee compensation plans were included in the calculation of diluted earnings per share.  For those same periods, 1 thousand, 8 thousand and 1 thousand potential shares attributable to exercises or conversions into common stock under stock-based employee compensation plans were not included in the calculation of diluted earnings per share, because the effect would have been antidilutive.Supplementary Cash Flow InformationCash payments made for interest were $110 million, $124 million and $136 million for the years ended December 31, 2021, 2020 and 2019.  Cash payments made for income taxes were $278 million, $108 million and $255 million for the years ended December 31, 2021, 2020 and 2019. |

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No definition available.
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| - Definition
The entire disclosure for all significant accounting policies of the reporting entity.
+ References
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