| **Reinsurance (Details) - USD ($) $ in Millions**             | 12 Months Ended |
|---------------------------------------------------------------|-----------------|
||
| **SEC Schedule, 12-17, Insurance Companies, Reinsurance**     |            |   |   |
| Gross amounts, life insurance in force                        | $ 122,053       | $ 120,147 | $ 116,697 |
| Gross amounts                                                 | 7,801           | 7,056 | 6,366 |
| Ceded amounts to other companies, life insurance in force     | 39,692          | 39,665 | 39,204 |
| Ceded premiums earned                                         | 412             | 392 | 331 |
| Assumed amounts from other companies, life insurance in force | 0               | 0 | 0 |
| Assumed amounts from other companies                          | 569             | 561 | 443 |
| Net amounts, life insurance in force                          | 82,361          | 80,482 | 77,493 |
| Premiums Earned, Net                                          | $ 7,958         | $ 7,225 | $ 6,478 |
| Percentage of amounts assumed to net, life insurance in force | 0.00%           | 0.00% | 0.00% |
| Percentage of amounts assumed to net                          | 7.20%           | 7.80% | 6.80% |
| Commercial Insurance                                          |            |   |   |
| **SEC Schedule, 12-17, Insurance Companies, Reinsurance**     |            |   |   |
| Gross amounts                                                 | $ 4,399         | $ 4,150 | $ 3,777 |
| Ceded premiums earned                                         | 147             | 137 | 115 |
| Assumed amounts from other companies                          | 12              | 11 | 12 |
| Premiums Earned, Net                                          | $ 4,264         | $ 4,024 | $ 3,674 |
| Percentage of amounts assumed to net                          | 0.30%           | 0.30% | 0.30% |
| Personal Insurance                                            |            |   |   |
| **SEC Schedule, 12-17, Insurance Companies, Reinsurance**     |            |   |   |
| Gross amounts                                                 | $ 2,117         | $ 1,755 | $ 1,586 |
| Ceded premiums earned                                         | 74              | 67 | 45 |
| Assumed amounts from other companies                          | 1               | 1 | 1 |
| Premiums Earned, Net                                          | $ 2,044         | $ 1,689 | $ 1,542 |
| Percentage of amounts assumed to net                          | 0.00%           | 0.10% | 0.10% |
| Excess and Surplus Lines Insurance                            |            |   |   |
| **SEC Schedule, 12-17, Insurance Companies, Reinsurance**     |            |   |   |
| Gross amounts                                                 | $ 572           | $ 510 | $ 417 |
| Ceded premiums earned                                         | 30              | 25 | 19 |
| Assumed amounts from other companies                          | 0               | 0 | 0 |
| Premiums Earned, Net                                          | $ 542           | $ 485 | $ 398 |
| Percentage of amounts assumed to net                          | 0.00%           | 0.00% | 0.00% |
| Reinsurance assumed and other non segment                     |            |   |   |
| **SEC Schedule, 12-17, Insurance Companies, Reinsurance**     |            |   |   |
| Gross amounts                                                 | $ 319           | $ 262 | $ 216 |
| Ceded premiums earned                                         | 80              | 85 | 76 |
| Assumed amounts from other companies                          | 556             | 549 | 430 |
| Premiums Earned, Net                                          | $ 795           | $ 726 | $ 570 |
| Percentage of amounts assumed to net                          | 69.90%          | 75.60% | 75.40% |
| Property, Liability and Casualty Insurance                    |            |   |   |
| **SEC Schedule, 12-17, Insurance Companies, Reinsurance**     |            |   |   |
| Gross amounts                                                 | $ 7,407         | $ 6,677 | $ 5,996 |
| Ceded premiums earned                                         | 331             | 314 | 255 |
| Assumed amounts from other companies                          | 569             | 561 | 443 |
| Premiums Earned, Net                                          | $ 7,645         | $ 6,924 | $ 6,184 |
| Percentage of amounts assumed to net                          | 7.40%           | 8.10% | 7.20% |
| Life Insurance Segment                                        |            |   |   |
| **SEC Schedule, 12-17, Insurance Companies, Reinsurance**     |            |   |   |
| Gross amounts                                                 | $ 394           | $ 379 | $ 370 |
| Ceded premiums earned                                         | 81              | 78 | 76 |
| Assumed amounts from other companies                          | 0               | 0 | 0 |
| Premiums Earned, Net                                          | $ 313           | $ 301 | $ 294 |
| Percentage of amounts assumed to net                          | 0.00%           | 0.00% | 0.00% |

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|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of life insurance issued and outstanding assumed from other entity, as disclosed in supplementary reinsurance information. Includes, but is not limited to, dividend and adjustment to face value.
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| - Definition
Amount of life insurance issued and outstanding ceded to other entity, as disclosed in supplementary reinsurance information. Includes, but is not limited to, dividend and adjustment to face value.
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|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount, before effect of reinsurance, of life insurance issued and outstanding, as disclosed in supplementary reinsurance information. Includes, but is not limited to, dividend and adjustment to face value.
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|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount, after effect of reinsurance, of life insurance issued and outstanding, as disclosed in supplementary reinsurance information. Includes, but is not limited to, dividend and adjustment to face value.
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|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Percentage of assumed life insurance contract issued and outstanding to life insurance contract issued and outstanding after effect of reinsurance, as disclosed in supplementary reinsurance information. Includes, but is not limited to, dividend and adjustment to face value.
+ References
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| - Definition
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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|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of earned premiums assumed from other entities.
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|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of earned premiums ceded to other entities.
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|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount, before premiums ceded to other entities and premiums assumed by the entity, of premiums earned.
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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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| - Definition
Percentage of assumed premium earned to premium earned after effects of reinsurance, as disclosed in supplementary reinsurance information.
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