| **Fair Value (Table of reconciliation for assets and liabilities measured at fair value on a recurring basis using significant unobservable inputs) (Details) - USD ($) $ in Millions** | 3 Months Ended | 9 Months Ended |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|----------------|----------------|
||
| **Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]**                                                                       |           |           |   |   |
| Balance, Beginning, Assets                                                                                                                                                              | $ 1,580        | $ 1,375        | $ 1,578 | $ 1,151 |
| Reported in Net investment gains (losses)                                                                                                                                               | (1)            | (2)            | (1) | (11) |
| Reported in Other comprehensive income (loss)                                                                                                                                           | (92)           | 2              | (339) | (27) |
| Total realized and unrealized investment gains (losses)                                                                                                                                 | (91)           | 2              | (329) | (32) |
| Purchases                                                                                                                                                                               | 125            | 139            | 487 | 429 |
| Sales                                                                                                                                                                                   | 0              | (20)           | (10) | (27) |
| Settlements                                                                                                                                                                             | (18)           | (22)           | (108) | (74) |
| Transfers into Level 3                                                                                                                                                                  | 47             | 52             | 76 | 92 |
| Transfers out of Level 3                                                                                                                                                                | (53)           | (90)           | (104) | (103) |
| Balance, Ending, Assets                                                                                                                                                                 | 1,590          | 1,436          | 1,590 | 1,436 |
| Unrealized gains (losses) on Level 3 assets and liabilities recognized in Net income (loss) in the period                                                                               | (7)            | (3)            | (8) | (1) |
| Unrealized gains (losses) on Level 3 assets and liabilities recognized in Other comprehensive income (loss) in the period                                                               | (93)           | 2              | (338) | (27) |
| Corporate and other bonds                                                                                                                                                               |           |           |   |   |
| **Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]**                                                                       |           |           |   |   |
| Balance, Beginning, Assets                                                                                                                                                              | 846            | 883            | 937 | 770 |
| Reported in Net investment gains (losses)                                                                                                                                               | 0              | 1              | (2) | (9) |
| Reported in Other comprehensive income (loss)                                                                                                                                           | (50)           | 1              | (203) | (23) |
| Total realized and unrealized investment gains (losses)                                                                                                                                 | (49)           | 2              | (204) | (32) |
| Purchases                                                                                                                                                                               | 9              | 55             | 127 | 219 |
| Sales                                                                                                                                                                                   | 0              | 0              | (5) | (3) |
| Settlements                                                                                                                                                                             | (4)            | (11)           | (63) | (35) |
| Transfers into Level 3                                                                                                                                                                  | 0              | 0              | 10 | 10 |
| Transfers out of Level 3                                                                                                                                                                | 0              | (52)           | 0 | (52) |
| Balance, Ending, Assets                                                                                                                                                                 | 802            | 877            | 802 | 877 |
| Unrealized gains (losses) on Level 3 assets and liabilities recognized in Net income (loss) in the period                                                                               | 0              | 0              | 0 | 0 |
| Unrealized gains (losses) on Level 3 assets and liabilities recognized in Other comprehensive income (loss) in the period                                                               | (51)           | 2              | (203) | (22) |
| States, municipalities and political subdivisions                                                                                                                                       |           |           |   |   |
| **Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]**                                                                       |           |           |   |   |
| Balance, Beginning, Assets                                                                                                                                                              | 46             | 57             | 56 | 46 |
| Reported in Net investment gains (losses)                                                                                                                                               | 0              | 0              | 0 | 0 |
| Reported in Other comprehensive income (loss)                                                                                                                                           | (4)            | 0              | (14) | 0 |
| Total realized and unrealized investment gains (losses)                                                                                                                                 | (4)            | 0              | (14) | 0 |
| Purchases                                                                                                                                                                               | 0              | 0              | 0 | 12 |
| Sales                                                                                                                                                                                   | 0              | 0              | 0 | 0 |
| Settlements                                                                                                                                                                             | 0              | 0              | 0 | (1) |
| Transfers into Level 3                                                                                                                                                                  | 0              | 0              | 0 | 0 |
| Transfers out of Level 3                                                                                                                                                                | 0              | 0              | 0 | 0 |
| Balance, Ending, Assets                                                                                                                                                                 | 42             | 57             | 42 | 57 |
| Unrealized gains (losses) on Level 3 assets and liabilities recognized in Net income (loss) in the period                                                                               | 0              | 0              | 0 | 0 |
| Unrealized gains (losses) on Level 3 assets and liabilities recognized in Other comprehensive income (loss) in the period                                                               | (4)            | 0              | (14) | 0 |
| Asset-backed                                                                                                                                                                            |           |           |   |   |
| **Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]**                                                                       |           |           |   |   |
| Balance, Beginning, Assets                                                                                                                                                              | 641            | 410            | 556 | 308 |
| Reported in Net investment gains (losses)                                                                                                                                               | 2              | 0              | 7 | 0 |
| Reported in Other comprehensive income (loss)                                                                                                                                           | (38)           | 1              | (122) | (4) |
| Total realized and unrealized investment gains (losses)                                                                                                                                 | (31)           | 2              | (104) | 0 |
| Purchases                                                                                                                                                                               | 116            | 83             | 348 | 197 |
| Sales                                                                                                                                                                                   | 0              | (9)            | (2) | (9) |
| Settlements                                                                                                                                                                             | (14)           | (11)           | (54) | (38) |
| Transfers into Level 3                                                                                                                                                                  | 47             | 41             | 66 | 71 |
| Transfers out of Level 3                                                                                                                                                                | (43)           | (38)           | (94) | (51) |
| Balance, Ending, Assets                                                                                                                                                                 | 716            | 478            | 716 | 478 |
| Unrealized gains (losses) on Level 3 assets and liabilities recognized in Net income (loss) in the period                                                                               | 0              | 0              | 0 | 0 |
| Unrealized gains (losses) on Level 3 assets and liabilities recognized in Other comprehensive income (loss) in the period                                                               | (38)           | 0              | (121) | (5) |
| Equity securities                                                                                                                                                                       |           |           |   |   |
| **Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]**                                                                       |           |           |   |   |
| Balance, Beginning, Assets                                                                                                                                                              | 47             | 25             | 29 | 27 |
| Reported in Net investment gains (losses)                                                                                                                                               | (3)            | (3)            | (6) | (2) |
| Reported in Other comprehensive income (loss)                                                                                                                                           | 0              | 0              | 0 | 0 |
| Total realized and unrealized investment gains (losses)                                                                                                                                 | (7)            | (2)            | (7) | 0 |
| Purchases                                                                                                                                                                               | 0              | 1              | 12 | 1 |
| Sales                                                                                                                                                                                   | 0              | (11)           | (3) | (15) |
| Settlements                                                                                                                                                                             | 0              | 0              | 9 | 0 |
| Transfers into Level 3                                                                                                                                                                  | 0              | 11             | 0 | 11 |
| Transfers out of Level 3                                                                                                                                                                | (10)           | 0              | (10) | 0 |
| Balance, Ending, Assets                                                                                                                                                                 | 30             | 24             | 30 | 24 |
| Unrealized gains (losses) on Level 3 assets and liabilities recognized in Net income (loss) in the period                                                                               | (7)            | (3)            | (8) | (1) |
| Unrealized gains (losses) on Level 3 assets and liabilities recognized in Other comprehensive income (loss) in the period                                                               | 0              | 0              | 0 | 0 |
| Reported in Net investment income                                                                                                                                                       |           |           |   |   |
| **Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]**                                                                       |           |           |   |   |
| Reported in Net investment income                                                                                                                                                       | 2              | 2              | 11 | 6 |
| Reported in Net investment income | Corporate and other bonds                                                                                                                           |           |           |   |   |
| **Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]**                                                                       |           |           |   |   |
| Reported in Net investment income                                                                                                                                                       | 1              | 0              | 1 | 0 |
| Reported in Net investment income | States, municipalities and political subdivisions                                                                                                   |           |           |   |   |
| **Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]**                                                                       |           |           |   |   |
| Reported in Net investment income                                                                                                                                                       | 0              | 0              | 0 | 0 |
| Reported in Net investment income | Asset-backed                                                                                                                                        |           |           |   |   |
| **Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]**                                                                       |           |           |   |   |
| Reported in Net investment income                                                                                                                                                       | 5              | 1              | 11 | 4 |
| Reported in Net investment income | Equity securities                                                                                                                                   |           |           |   |   |
| **Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]**                                                                       |           |           |   |   |
| Reported in Net investment income                                                                                                                                                       | $ (4)          | $ 1            | $ (1) | $ 2 |

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Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss), Included In Earnings And Other Comprehensive Income (Loss)
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No definition available.
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Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Net Investment Income
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No definition available.
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Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Unrealized Gain (Loss) Included in Other Comprehensive Income (Loss)
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| - Definition
Amount of unrealized gain (loss) recognized in income from asset measured at fair value on recurring basis using unobservable input (level 3) and still held.
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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.
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| - Definition
Amount of gain (loss) recognized in income from asset measured at fair value on recurring basis using unobservable input (level 3).
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| - Definition
Amount of gain (loss) recognized in other comprehensive income (OCI) from asset measured at fair value on recurring basis using unobservable input (level 3).
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Amount of purchases of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.
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Amount of sale of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.
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Amount of settlement of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.
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Amount of transfer of financial instrument classified as an asset into level 3 of the fair value hierarchy.
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Amount of transfers of financial instrument classified as an asset out of level 3 of the fair value hierarchy.
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