| **Deferred Policy Acquisition Costs - Deferred Policy Acquisition Costs and Asset Reconciliation (Detail) - USD ($) $ in Millions** | 3 Months Ended |
|-------------------------------------------------------------------------------------------------------------------------------------|----------------|
||
| **Movement Analysis of Deferred Policy Acquisition Costs**                                                                          |           |   |
| Deferred policy acquisition costs asset, beginning of period                                                                        | $ 1,093        | $ 1,013 |
| Capitalized deferred policy acquisition costs                                                                                       | 417            | 383 |
| Amortized deferred policy acquisition costs                                                                                         | (367)          | (348) |
| Deferred policy acquisition costs asset, end of period                                                                              | 1,143          | 1,048 |
| Consolidated Property And Casualty Insurance                                                                                        |           |   |
| **Movement Analysis of Deferred Policy Acquisition Costs**                                                                          |           |   |
| Deferred policy acquisition costs asset, beginning of period                                                                        | 749            | 682 |
| Capitalized deferred policy acquisition costs                                                                                       | 407            | 372 |
| Amortized deferred policy acquisition costs                                                                                         | (360)          | (340) |
| Deferred policy acquisition costs asset, end of period                                                                              | 796            | 714 |
| Life Insurance Segment                                                                                                              |           |   |
| **Movement Analysis of Deferred Policy Acquisition Costs**                                                                          |           |   |
| Deferred policy acquisition costs asset, beginning of period                                                                        | 344            | 331 |
| Capitalized deferred policy acquisition costs                                                                                       | 10             | 11 |
| Amortized deferred policy acquisition costs                                                                                         | (7)            | (8) |
| Deferred policy acquisition costs asset, end of period                                                                              | $ 347          | $ 334 |

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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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