| **Deferred Policy Acquisition Costs - Deferred Policy Acquisition Costs and Asset Reconciliation (Detail) - USD ($) $ in Millions** | 12 Months Ended |
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| **Movement Analysis of Deferred Policy Acquisition Costs**                                                                          |            |   |   |
| Deferred policy acquisition costs asset, beginning of period                                                                        | $ 1,013         | $ 916 | $ 838 |
| Deferred Policy Acquisition Cost, Capitalization                                                                                    | 1,530           | 1,427 | 1,254 |
| Deferred Policy Acquisition Costs, Amortization Expense                                                                             | (1,450)         | (1,330) | (1,176) |
| Deferred policy acquisition costs asset, end of period                                                                              | 1,093           | 1,013 | 916 |
| Consolidated Property And Casualty Insurance Entity                                                                                 |            |   |   |
| **Movement Analysis of Deferred Policy Acquisition Costs**                                                                          |            |   |   |
| Deferred policy acquisition costs asset, beginning of period                                                                        | 682             | 602 | 542 |
| Deferred Policy Acquisition Cost, Capitalization                                                                                    | 1,488           | 1,383 | 1,211 |
| Deferred Policy Acquisition Costs, Amortization Expense                                                                             | (1,421)         | (1,303) | (1,151) |
| Deferred policy acquisition costs asset, end of period                                                                              | 749             | 682 | 602 |
| Life Insurance Segment                                                                                                              |            |   |   |
| **Movement Analysis of Deferred Policy Acquisition Costs**                                                                          |            |   |   |
| Deferred policy acquisition costs asset, beginning of period                                                                        | 331             | 314 | 296 |
| Deferred Policy Acquisition Cost, Capitalization                                                                                    | 42              | 44 | 43 |
| Deferred Policy Acquisition Costs, Amortization Expense                                                                             | (29)            | (27) | (25) |
| Deferred policy acquisition costs asset, end of period                                                                              | $ 344           | $ 331 | $ 314 |

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| - Definition
Amount of amortization expense (reversal of expense) for deferred policy acquisition costs.
+ References
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|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of deferred policy acquisition cost capitalized on contract remaining in force.
+ References
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|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of deferred policy acquisition cost capitalized.
+ References
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| - Definition
A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.
+ References
No definition available.
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