| **Investments (Net investment income) (Details) - USD ($) $ in Millions** | 12 Months Ended |
|---------------------------------------------------------------------------|-----------------|
||
| **Net Investment Income [Line Items]**                                    |            |   |   |
| Gross investment income                                                   | $ 2,343         | $ 1,877 | $ 2,223 |
| Investment expense                                                        | (79)            | (72) | (64) |
| Net investment income                                                     | 2,264           | 1,805 | 2,159 |
| Fixed maturity securities                                                 |            |   |   |
| **Net Investment Income [Line Items]**                                    |            |   |   |
| Gross investment income                                                   | 1,941           | 1,787 | 1,707 |
| Equity securities                                                         |            |   |   |
| **Net Investment Income [Line Items]**                                    |            |   |   |
| Gross investment income                                                   | 63              | 23 | 83 |
| Limited partnership investments                                           |            |   |   |
| **Net Investment Income [Line Items]**                                    |            |   |   |
| Gross investment income                                                   | 174             |   | 362 |
| Gross investment loss                                                     |            | (12) |   |
| Mortgage loans                                                            |            |   |   |
| **Net Investment Income [Line Items]**                                    |            |   |   |
| Gross investment income                                                   | 58              | 54 | 61 |
| Short-term investments                                                    |            |   |   |
| **Net Investment Income [Line Items]**                                    |            |   |   |
| Gross investment income                                                   | 75              | 16 | 1 |
| Trading portfolio                                                         |            |   |   |
| **Net Investment Income [Line Items]**                                    |            |   |   |
| Gross investment income                                                   | 4               | 4 | 9 |
| Other                                                                     |            |   |   |
| **Net Investment Income [Line Items]**                                    |            |   |   |
| Gross investment income                                                   | 28              | 5 | 0 |
| Common Stock                                                              |            |   |   |
| **Net Investment Income [Line Items]**                                    |            |   |   |
| Equity securities, FV-NI, gain (loss)                                     | 11              | 47 | 28 |
| Non-redeemable preferred stock                                            |            |   |   |
| **Net Investment Income [Line Items]**                                    |            |   |   |
| Equity securities, FV-NI, gain (loss)                                     | $ 14            | $ (75) | $ 2 |

| X                                                                                                                                                                                                                                                 |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Gross Investment Loss, Operating
+ 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).
+ References
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|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount, before investment expense, of income earned from investments in securities and real estate. Includes, but is not limited to, real estate investment, policy loans, dividends, and interest. Excludes realized gain (loss) on investments.
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| - Definition
Amount of expenses related to the generation of investment income.
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|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount, after investment expense, of income earned from investments in securities and real estate. Includes, but is not limited to, real estate investment, policy loans, dividends, and interest. Excludes realized gain (loss) on investments.
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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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