| **Schedule VI. Supplemental Information Concerning Property and Casualty Insurance Operations (Details) (Consolidated Property and Casualty Insurance Entity [Member], USD $)In Millions, unless otherwise specified** | 12 Months Ended |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|-----------------|
||
| Consolidated Property and Casualty Insurance Entity [Member]                                                                                                                                                           |            |   |   |
| Deferred acquisition costs                                                                                                                                                                                             | $ 624           | $ 598 |    |
| Reserves for unpaid claim and claim adjustment expenses                                                                                                                                                                | 24,015          | 24,696 |    |
| Discount deducted from claim and claim adjustment expense reserves above (based on interest rates ranging from 3.0% to 9.7%)                                                                                           | 1,586           | 1,850 |    |
| Unearned Premiums                                                                                                                                                                                                      | 3,718           | 3,610 |    |
| Net written premiums                                                                                                                                                                                                   | 7,348           | 6,964 | 6,798 |
| Net earned premiums                                                                                                                                                                                                    | 7,271           | 6,881 | 6,603 |
| Net investment income                                                                                                                                                                                                  | 2,240           | 2,074 | 1,845 |
| Incurred claim and claim adjustment expenses related to current year                                                                                                                                                   | 5,113           | 5,266 | 4,901 |
| Incurred claim and claim adjustment expenses related to prior years                                                                                                                                                    | (115)           | (180) | (429) |
| Amortization of deferred acquisition costs                                                                                                                                                                             | 1,362           | 1,274 | 1,176 |
| Paid claim and claim adjustment expenses                                                                                                                                                                               | $ 5,566         | $ 5,257 | $ 4,499 |
| **Supplemental Information Parenthetical**                                                                                                                                                                             |            |   |   |
| Minimum interest rate in discount range                                                                                                                                                                                | 3.00%           |   |   |
| Maximum interest rate in discount range                                                                                                                                                                                | 9.70%           |   |   |

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|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of amortization expense on deferred policy acquisition cost.
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of insurance benefit, claims, loss and settlement expenses paid to the policyholders during the current accounting period.
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|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - 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                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - 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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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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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of net investment income earned by property-casualty insurance underwriter.
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - 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 insurance benefit, claims, loss and settlement expenses paid to the policyholders during the prior accounting period.
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - 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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