| **Legal Proceedings and Contingent Liabilities**            | 9 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
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| **Legal Proceedings and Contingent Liabilities [Abstract]** |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
| Legal Proceedings and Contingent Liabilities                | Note F. Legal Proceedings and Contingent LiabilitiesCNA 401(k) Plus Plan LitigationIn September 2016, a class action lawsuit was filed against CCC, Continental Assurance Company (CAC), CNAF, the Investment Committee of the CNA 401(k) Plus Plan, The Northern Trust Company and John Does 1-10 (collectively Defendants) over the CNA 401(k) Plus Plan.  The complaint alleges that Defendants breached fiduciary duties to the CNA 401(k) Plus Plan and caused prohibited transactions in violation of The Employee Retirement Income Security Act of 1974 when the CNA Fixed Income Fund’s annuity contract with CAC was canceled.  The plaintiff alleges he and a proposed class of the CNA 401(k) Plus Plan participants who had invested in the Fixed Income Fund suffered lower returns in their CNA 401(k) Plus Plan investments as a consequence of these alleged violations and seeks relief on behalf of the putative class.  Management has only recently begun evaluating the lawsuit as this litigation is in its preliminary stages, and as of yet no class has been certified.  CCC and the other Defendants are contesting the case and management currently is unable to predict the final outcome or the impact on the Company’s financial condition, results of operations, or cash flows.  As of September 30, 2016, the likelihood of loss is reasonably possible, but the amount of loss, if any, cannot be estimated at this stage of the litigation.Other LitigationThe Company is a party to other routine litigation incidental to its business, which, based on the facts and circumstances currently known, is not material to the Condensed Consolidated Financial Statements. |

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Legal Proceedings and Contingent Liabilities [Abstract]
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The entire disclosure for legal proceedings, legal contingencies, litigation, regulatory and environmental matters and other contingencies.
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