| **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                                                              | $ 5,025         | $ 4,934 | $ 5,043 |
| Incurred claim and claim adjustment expenses related to prior years                                                               | (342)           | (255) | (36) |
| Consolidated Property and Casualty Insurance Entity [Member]                                                                      |            |   |   |
| Deferred acquisition costs                                                                                                        | 599             | 597 |   |
| Reserves for unpaid claim and claim adjustment expenses                                                                           | 22,343          | 22,663 |   |
| Discount deducted from claim and claim adjustment expense reserves above (based on interest rates ranging from 3.5% to 8.0%)      | 1,572           | 1,534 |   |
| Unearned Premiums                                                                                                                 | 3,762           | 3,671 |   |
| Net written premiums                                                                                                              | 6,988           | 6,962 | 7,088 |
| Net earned premiums                                                                                                               | 6,924           | 6,921 | 7,212 |
| Net investment income                                                                                                             | 1,952           | 1,807 | 2,031 |
| Incurred claim and claim adjustment expenses related to current year                                                              | 5,025           | 4,934 | 5,043 |
| Incurred claim and claim adjustment expenses related to prior years                                                               | (342)           | (255) | (39) |
| Amortization of deferred acquisition costs                                                                                        | 1,235           | 1,540 | 1,317 |
| Paid claim and claim adjustment expenses                                                                                          | $ 5,134         | $ 4,945 | $ 5,297 |
| Consolidated Property and Casualty Insurance Entity [Member] | Minimum [Member]                                                   |            |   |   |
| **Supplemental Information Parenthetical**                                                                                        |            |   |   |
| Supplemental Information for Property, Casualty Insurance Underwriters, Interest Rate at which Discount Computed                  | 3.50%           | 3.50% |   |
| Consolidated Property and Casualty Insurance Entity [Member] | Maximum [Member]                                                   |            |   |   |
| **Supplemental Information Parenthetical**                                                                                        |            |   |   |
| Supplemental Information for Property, Casualty Insurance Underwriters, Interest Rate at which Discount Computed                  | 8.00%           | 8.00% |   |

| X                                                                                                                                                                                                                                                                                                   |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
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, after effects of reinsurance, 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.
+ References
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The amount of discount that may be deducted from the reserve for unpaid claims and claims adjustment expense.
+ References
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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 rate at which the discount was computed for each business segment reported.
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| - Definition
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, after effects of reinsurance, 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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