| **Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions** | 3 Months Ended | 12 Months Ended |
|-------------------------------------------------------------------------------------------------|----------------|-----------------|
||
| **Liability for Catastrophe Claims [Line Items]**                                               |           |            |   |   |   |   |   |   |   |   |   |
| Revenues                                                                                        | $ 2,777        | $ 2,685         | $ 2,610 | $ 2,695 | $ 2,403 | $ 2,622 | $ 2,574 | $ 2,535 | $ 10,767 | $ 10,134 | $ 9,542 |
| Net income (loss)                                                                               | $ 273          | $ 107           | $ 278 | $ 342 | $ (84) | $ 336 | $ 270 | $ 291 | $ 1,000 | $ 813 | $ 899 |
| Basic earnings (loss) per share (in usd per share)                                              | $ 1.00         | $ 0.39          | $ 1.03 | $ 1.26 | $ (0.31) | $ 1.24 | $ 0.99 | $ 1.07 | $ 3.68 | $ 2.99 | $ 3.32 |
| Diluted earnings (loss) per share (in usd per share)                                            | $ 1.00         | $ 0.39          | $ 1.02 | $ 1.25 | $ (0.31) | $ 1.23 | $ 0.99 | $ 1.07 | $ 3.67 | $ 2.98 | $ 3.30 |
| Charge related to recognition of active life reserve premium deficiency                         |           | $ 170           |   |   |   |   |   |   |   |   |   |
| Hurricane Michael and California Wildfires                                                      |           |            |   |   |   |   |   |   |   |   |   |
| **Liability for Catastrophe Claims [Line Items]**                                               |           |            |   |   |   |   |   |   |   |   |   |
| Catastrophe losses net of reinsurance                                                           |           |            |   |   | $ 107 |   |   |   |   |   |   |
| Limited Partnership and Common Stock Investments [Member]                                       |           |            |   |   |   |   |   |   |   |   |   |
| **Liability for Catastrophe Claims [Line Items]**                                               |           |            |   |   |   |   |   |   |   |   |   |
| Loss on limited partnership and common stock investments                                        |           |            |   |   | $ 109 |   |   |   |   |   |   |

| X                                                                                                                                                                                                                                                           |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Catastrophe losses net of reinsurance
+ References
No definition available.
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|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.
+ References
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|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.
+ References
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| - Definition
Amount of unrealized and realized gain (loss) on investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).
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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
The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.
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|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of expense for premium deficiency and loss recognition testing on long-duration contract issued by insurance entity. Excludes closed block.
+ References
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|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).
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