| **Schedule VI. Supplemental Information Concerning Property and Casualty Insurance Operations (Details) - USD ($) $ in Millions** | 12 Months Ended |
|-----------------------------------------------------------------------------------------------------------------------------------|-----------------|
||
| Incurred claim and claim adjustment expenses related to current year                                                              | $ 4,934         | $ 5,043 | $ 5,114 |
| Incurred claim and claim adjustment expenses related to prior years                                                               | (255)           | (36) | $ (115) |
| Consolidated Property and Casualty Insurance Entity [Member]                                                                      |            |   |   |
| Deferred acquisition costs                                                                                                        | 597             | 600 |  |
| Reserves for unpaid claim and claim adjustment expenses                                                                           | 22,663          | 23,271 |  |
| Discount deducted from claim and claim adjustment expense reserves above (based on interest rates ranging from 3.5% to 8.0%)      | 1,534           | 1,578 |  |
| Unearned Premiums                                                                                                                 | 3,671           | 3,592 |  |
| Net written premiums                                                                                                              | 6,962           | 7,088 | $ 7,348 |
| Net earned premiums                                                                                                               | 6,921           | 7,212 | 7,271 |
| Net investment income                                                                                                             | 1,807           | 2,031 | 2,240 |
| Incurred claim and claim adjustment expenses related to current year                                                              | 4,934           | 5,043 | 5,113 |
| Incurred claim and claim adjustment expenses related to prior years                                                               | (255)           | (39) | (115) |
| Amortization of deferred acquisition costs                                                                                        | 1,540           | 1,317 | 1,362 |
| Paid claim and claim adjustment expenses                                                                                          | $ 4,945         | $ 5,297 | $ 5,566 |
| **Supplemental Information Parenthetical**                                                                                        |            |   |   |
| Minimum interest rate in discount range                                                                                           | 3.50%           | 3.50% | 3.50% |
| Maximum interest rate in discount range                                                                                           | 8.00%           | 8.00% | 8.00% |

| X                                                                                                                                                                                                                                                                                                   |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
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Schedule Vi Supplemental Information Parenthetical [Abstract]
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| - Definition
Amount of amortization expense on deferred policy acquisition cost.
+ References
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| - Definition
Amount of expense for claims incurred in the current reporting period and related claims settlement costs.
+ References
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of deferred policy acquisition cost related to property-casualty insurance policy written.
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The amount of discount that may be deducted from the reserve for unpaid claims and claims adjustment expense.
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
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| - Definition
Amount of property-casualty insurance premium revenue earned on insurance policies.
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|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The maximum interest rate in the range of rates estimated at which the discount was computed for each business segment reported.
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| - Definition
The minimum interest rate in the range of rates estimated at which the discount was computed for each business segment reported.
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Amount of net investment income earned by property-casualty insurance underwriter.
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|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Payments of claims and claims adjustment expenses during the period of a property-casualty insurance entity.
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| - Definition
Amount of actual premium written by property-casualty insurance underwriter.
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| - Definition
Amount of expense (reversal of expense) for claims incurred in prior reporting periods and related claims settlement costs.
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| - Definition
The amount of reserve, policy claim payable and loss expense incurred by property-casualty insurance underwriter.
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| - Definition
Amount of property-casualty insurance premium revenue not yet earned on insurance policies.
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