| **Investments (Narrative) (Details) - USD ($)**                                             | 3 Months Ended  | 9 Months Ended |                 |
|---------------------------------------------------------------------------------------------|-----------------|----------------|-----------------|
||
| **Net Investment Income [Line Items]**                                                      |            |           |            |   |   |
| Reduction of net unrealized gains on investments included in AOCI due to shadow adjustments | $ 1,115,000,000 |           | $ 1,115,000,000 |   | $ 1,411,000,000 |
| Derivative, notional amount                                                                 | 174,000,000     |           | 174,000,000     |   | 167,000,000 |
| Derivative fair value                                                                       | 6,000,000       |           | 6,000,000       |   |   |
| Derivative fair value                                                                       |            |           |            |   | $ 3,000,000 |
| Future capital call commitments for limited partnership investments                         | 605,000,000     |           | 605,000,000     |   |   |
| Mortgage loan commitments                                                                   | 16,000,000      |           | 16,000,000      |   |   |
| Commitments to purchase or fund privately placed debt securities                            | 282,000,000     |           | 282,000,000     |   |   |
| Commitments to sell various privately placed debt securities                                | 87,000,000      |           | 87,000,000      |   |   |
| Common Stock                                                                                |            |           |            |   |   |
| **Net Investment Income [Line Items]**                                                      |            |           |            |   |   |
| Net realized investment gains (losses)                                                      | (2,000,000)     |           | (2,000,000)     |   |   |
| Preferred stock                                                                             |            |           |            |   |   |
| **Net Investment Income [Line Items]**                                                      |            |           |            |   |   |
| Net realized investment gains (losses)                                                      | $ 2,000,000     |           | $ (23,000,000)  |   |   |
| Senior notes 7.350%, face amount $350, due November 15, 2019 | Senior Notes                 |            |           |            |   |   |
| **Net Investment Income [Line Items]**                                                      |            |           |            |   |   |
| Net realized investment gains (losses)                                                      |            | $ (42,000,000) |            | $ (42,000,000) |   |
| Senior notes redeemed                                                                       |            | $ 350,000,000  |            | $ 350,000,000 |   |

| X                                                                                                                                                                                                                                                                                   |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Commitments To Purchase Or Fund Additional Amounts
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| - Definition
Commitments To Sell Various Privately Placed Debt Securities
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No definition available.
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|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Future capital call commitments to limited partnerships for which we would receive an ownership interest.
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|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Mortgage loan commitments, representing signed loan applications received and accepted.
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Reduction of net unrealized gains on investments included in AOCI due to shadow adjustments
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| - Definition
Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.
+ References
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| - Definition
Face (par) amount of debt instrument at time of issuance.
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|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Fair value, before effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.
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| - Definition
Fair value of asset associated with financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset.
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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
The net realized gains or losses on investments during the period, not including gains or losses on securities separately or otherwise categorized as trading, available-for-sale, or held-to-maturity.
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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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