| **Reinsurance (Details) - USD ($) $ in Millions**                                 | 12 Months Ended |
|-----------------------------------------------------------------------------------|-----------------|
||
| **Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]** |            |   |   |
| Gross amounts, life insurance in force                                            | $ 99,888        | $ 95,533 | $ 91,451 |
| Gross amounts                                                                     | 5,052           | 4,857 | 4,667 |
| Ceded amounts to other companies, life insurance in force                         | 38,711          | 38,724 | 38,716 |
| Ceded amounts to other companies                                                  | 230             | 224 | 216 |
| Assumed amounts from other companies, life insurance in force                     | 0               | 0 | 0 |
| Assumed amounts from other companies                                              | 132             | 77 | 29 |
| Net amounts, life insurance in force                                              | 61,177          | 56,808 | 52,735 |
| Premiums Earned, Net                                                              | $ 4,954         | $ 4,710 | $ 4,480 |
| Percentage of amounts assumed to net, life insurance in force                     | 0.00%           | 0.00% | 0.00% |
| Percentage of amounts assumed to net                                              | 2.70%           | 1.60% | 0.70% |
| Commercial Insurance                                                              |            |   |   |
| **Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]** |            |   |   |
| Gross amounts                                                                     | $ 3,258         | $ 3,180 | $ 3,088 |
| Ceded amounts to other companies                                                  | 99              | 98 | 102 |
| Assumed amounts from other companies                                              | 6               | 7 | 10 |
| Premiums Earned, Net                                                              | $ 3,165         | $ 3,089 | $ 2,996 |
| Percentage of amounts assumed to net                                              | 0.20%           | 0.20% | 0.30% |
| Personal Insurance                                                                |            |   |   |
| **Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]** |            |   |   |
| Gross amounts                                                                     | $ 1,275         | $ 1,195 | $ 1,131 |
| Ceded amounts to other companies                                                  | 35              | 35 | 35 |
| Assumed amounts from other companies                                              | 1               | 1 | 1 |
| Premiums Earned, Net                                                              | $ 1,241         | $ 1,161 | $ 1,097 |
| Percentage of amounts assumed to net                                              | 0.10%           | 0.10% | 0.10% |
| Excess and Surplus Lines Insurance                                                |            |   |   |
| **Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]** |            |   |   |
| Gross amounts                                                                     | $ 219           | $ 192 | $ 177 |
| Ceded amounts to other companies                                                  | 10              | 9 | 9 |
| Assumed amounts from other companies                                              | 0               | 0 | 0 |
| Premiums Earned, Net                                                              | $ 209           | $ 183 | $ 168 |
| Percentage of amounts assumed to net                                              | 0.00%           | 0.00% | 0.00% |
| Reinsurance assumed and other non segment [Member]                                |            |   |   |
| **Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]** |            |   |   |
| Gross amounts                                                                     | $ 0             | $ 0 | $ 0 |
| Ceded amounts to other companies                                                  | 18              | 20 | 8 |
| Assumed amounts from other companies                                              | 125             | 69 | 18 |
| Premiums Earned, Net                                                              | $ 107           | $ 49 | $ 10 |
| Percentage of amounts assumed to net                                              | 116.10%         | 140.80% | 188.00% |
| Property, Liability And Casualty Insurance Segment [Member]                       |            |   |   |
| **Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]** |            |   |   |
| Gross amounts                                                                     | $ 4,752         | $ 4,567 | $ 4,396 |
| Ceded amounts to other companies                                                  | 162             | 162 | 154 |
| Assumed amounts from other companies                                              | 132             | 77 | 29 |
| Premiums Earned, Net                                                              | $ 4,722         | $ 4,482 | $ 4,271 |
| Percentage of amounts assumed to net                                              | 2.80%           | 1.70% | 0.70% |
| Life Insurance Segment                                                            |            |   |   |
| **Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]** |            |   |   |
| Gross amounts                                                                     | $ 300           | $ 290 | $ 271 |
| Ceded amounts to other companies                                                  | 68              | 62 | 62 |
| Assumed amounts from other companies                                              | 0               | 0 | 0 |
| Premiums Earned, Net                                                              | $ 232           | $ 228 | $ 209 |
| Percentage of amounts assumed to net                                              | 0.00%           | 0.00% | 0.00% |

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|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of earned premiums assumed from other entities.
+ References
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|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of earned premiums ceded to other entities.
+ References
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|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount, before premiums ceded to other entities and premiums assumed by the entity, of premiums earned.
+ References
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of life insurance issued and outstanding assumed from other entities. Includes, but not limited to, dividends and adjustments to face value.
+ References
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| - Definition
Amount of life insurance issued and outstanding ceded to other entities. Includes, but not limited to, dividends and adjustments to face value.
+ References
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|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount before contracts ceded to other entities and contracts assumed by the entity of life insurance issued and outstanding. Includes, but not limited to, dividends and adjustments to face value.
+ References
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|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount after contracts ceded to other entities and contracts assumed by the entity of life insurance issued and outstanding. Includes, but not limited to, dividends and adjustments to face value.
+ References
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|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Percentage of assumed life insurance issued and outstanding contracts to life insurance issued and outstanding after contracts ceded to other entities and contracts assumed by the entity. Includes, but not limited to, dividends and adjustments to face value.
+ References
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|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount, after premiums ceded to other entities and premiums assumed by the entity, of premiums earned.
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |
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| - Definition
Percentage of assumed premiums earned by the entity to net premiums earned.
+ References
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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.
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No definition available.
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