| **Investments (Narrative) (Details) - USD ($)**                                        | 3 Months Ended | 9 Months Ended |               |
|----------------------------------------------------------------------------------------|----------------|----------------|---------------|
||
| **Gain (Loss) on Securities [Line Items]**                                             |           |           |          |   |   |
| Investment and derivative, realized gain (loss), coinsurance agreement                 |           | $ 35,000,000   |          |   |   |
| Debt securities, available-for-sale, realized loss                                     | $ 49,000,000   | 134,000,000    | $ 141,000,000 | $ 222,000,000 |   |
| Embedded derivative, gain on embedded derivative                                       |           | 24,000,000     |          |   |   |
| Mortgage loan losses due to changes in expected credit losses                          | 5,000,000      | 8,000,000      | 11,000,000    | 8,000,000 |   |
| Commitments to purchase or fund privately placed debt securities                       | 1,555,000,000  |           | 1,555,000,000 |   |   |
| Commitments to sell various privately placed debt securities                           | 65,000,000     |           | 65,000,000    |   |   |
| Mortgage loans                                                                         |           |           |          |   |   |
| **Gain (Loss) on Securities [Line Items]**                                             |           |           |          |   |   |
| Financing receivable, accrued interest, after allowance for credit loss                | 4,000,000      |           | 4,000,000     |   |   |
| Fixed maturity securities                                                              |           |           |          |   |   |
| **Gain (Loss) on Securities [Line Items]**                                             |           |           |          |   |   |
| Debt securities, available-for-sale, accrued interest, after allowance for credit loss | $ 430,000,000  | 401,000,000    | $ 430,000,000 | $ 401,000,000 | $ 394,000,000 |
| Funds Withheld Liability Securities                                                    |           |           |          |   |   |
| **Gain (Loss) on Securities [Line Items]**                                             |           |           |          |   |   |
| Debt securities, available-for-sale, realized loss                                     |           | $ 59,000,000   |          |   |   |

| X                                                                                                                                                                                                                                                                                   |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Commitments To Purchase Or Fund Additional Amounts
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| X                                                                                                                                                                                                                                                                                                     |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Commitments To Sell Various Privately Placed Debt Securities
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No definition available.
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| X                                                                                                                                                                                                                                                                                                                       |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Investment And Derivative, Realized Gain (Loss), Coinsurance Agreement
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No definition available.
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|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount, after allowance for credit loss, of accrued interest on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).
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|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of realized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).
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| - Definition
Increase in the fair value of the embedded derivative or group of embedded derivatives included in earnings in the period.
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|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount, after allowance for credit loss, of accrued interest on financing receivable.
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|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of credit loss expense (reversal of expense) for financing receivable.
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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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