| **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** | 12 Months Ended                   |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|-----------------------------------|
||
| **Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]**                                                                       |                              |   |
| Balance, Beginning, Assets                                                                                                                                                              | $ 1,676                           | $ 1,578 |
| Reported in Net investment gains (losses)                                                                                                                                               | $ (4)                             | $ 1 |
| Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]                                | Net investment (losses) gains     | Net investment (losses) gains |
| Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Asset, Gain (Loss), Statement of Other Comprehensive Income or Comprehensive Income [Extensible Enumeration]     | Other comprehensive income (loss) | Other comprehensive income (loss) |
| Reported in Other comprehensive income (loss)                                                                                                                                           | $ 48                              | $ (323) |
| Total realized and unrealized investment gains (losses)                                                                                                                                 | 57                                | (308) |
| Purchases                                                                                                                                                                               | 467                               | 580 |
| Sales                                                                                                                                                                                   | (4)                               | (10) |
| Settlements                                                                                                                                                                             | (97)                              | (145) |
| Transfers into Level 3                                                                                                                                                                  | 34                                | 85 |
| Transfers out of Level 3                                                                                                                                                                | (119)                             | (104) |
| Balance, Ending, Assets                                                                                                                                                                 | 2,014                             | 1,676 |
| Unrealized gains (losses) on Level 3 assets and liabilities recognized in Net income (loss) in the period                                                                               | (7)                               | (4) |
| Unrealized gains (losses) on Level 3 assets and liabilities recognized in Other comprehensive income (loss) in the period                                                               | 48                                | (321) |
| Corporate and other bonds                                                                                                                                                               |                              |   |
| **Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]**                                                                       |                              |   |
| Balance, Beginning, Assets                                                                                                                                                              | 810                               | 937 |
| Reported in Net investment gains (losses)                                                                                                                                               | 0                                 | (2) |
| Reported in Other comprehensive income (loss)                                                                                                                                           | 38                                | (184) |
| Total realized and unrealized investment gains (losses)                                                                                                                                 | 38                                | (185) |
| Purchases                                                                                                                                                                               | 219                               | 137 |
| Sales                                                                                                                                                                                   | 0                                 | (5) |
| Settlements                                                                                                                                                                             | (33)                              | (84) |
| Transfers into Level 3                                                                                                                                                                  | 11                                | 10 |
| Transfers out of Level 3                                                                                                                                                                | 0                                 | 0 |
| Balance, Ending, Assets                                                                                                                                                                 | 1,045                             | 810 |
| Unrealized gains (losses) on Level 3 assets and liabilities recognized in Net income (loss) in the period                                                                               | 0                                 | 0 |
| Unrealized gains (losses) on Level 3 assets and liabilities recognized in Other comprehensive income (loss) in the period                                                               | 38                                | (183) |
| States, municipalities and political subdivisions                                                                                                                                       |                              |   |
| **Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]**                                                                       |                              |   |
| Balance, Beginning, Assets                                                                                                                                                              | 43                                | 56 |
| Reported in Net investment gains (losses)                                                                                                                                               | 0                                 | 0 |
| Reported in Other comprehensive income (loss)                                                                                                                                           | 1                                 | (13) |
| Total realized and unrealized investment gains (losses)                                                                                                                                 | 1                                 | (13) |
| Purchases                                                                                                                                                                               | 0                                 | 0 |
| Sales                                                                                                                                                                                   | 0                                 | 0 |
| Settlements                                                                                                                                                                             | 0                                 | 0 |
| Transfers into Level 3                                                                                                                                                                  | 0                                 | 0 |
| Transfers out of Level 3                                                                                                                                                                | 0                                 | 0 |
| Balance, Ending, Assets                                                                                                                                                                 | 44                                | 43 |
| Unrealized gains (losses) on Level 3 assets and liabilities recognized in Net income (loss) in the period                                                                               | 0                                 | 0 |
| Unrealized gains (losses) on Level 3 assets and liabilities recognized in Other comprehensive income (loss) in the period                                                               | 1                                 | (13) |
| Asset-backed                                                                                                                                                                            |                              |   |
| **Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]**                                                                       |                              |   |
| Balance, Beginning, Assets                                                                                                                                                              | 788                               | 556 |
| Reported in Net investment gains (losses)                                                                                                                                               | (4)                               | 9 |
| Reported in Other comprehensive income (loss)                                                                                                                                           | 9                                 | (126) |
| Total realized and unrealized investment gains (losses)                                                                                                                                 | 25                                | (101) |
| Purchases                                                                                                                                                                               | 248                               | 424 |
| Sales                                                                                                                                                                                   | 0                                 | (2) |
| Settlements                                                                                                                                                                             | (64)                              | (70) |
| Transfers into Level 3                                                                                                                                                                  | 23                                | 75 |
| Transfers out of Level 3                                                                                                                                                                | (119)                             | (94) |
| Balance, Ending, Assets                                                                                                                                                                 | 901                               | 788 |
| Unrealized gains (losses) on Level 3 assets and liabilities recognized in Net income (loss) in the period                                                                               | 0                                 | 0 |
| Unrealized gains (losses) on Level 3 assets and liabilities recognized in Other comprehensive income (loss) in the period                                                               | 9                                 | (125) |
| Equity securities                                                                                                                                                                       |                              |   |
| **Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]**                                                                       |                              |   |
| Balance, Beginning, Assets                                                                                                                                                              | 35                                | 29 |
| Reported in Net investment gains (losses)                                                                                                                                               | 0                                 | (6) |
| Reported in Other comprehensive income (loss)                                                                                                                                           | 0                                 | 0 |
| Total realized and unrealized investment gains (losses)                                                                                                                                 | (7)                               | (9) |
| Purchases                                                                                                                                                                               | 0                                 | 19 |
| Sales                                                                                                                                                                                   | (4)                               | (3) |
| Settlements                                                                                                                                                                             | 0                                 | 9 |
| Transfers into Level 3                                                                                                                                                                  | 0                                 | 0 |
| Transfers out of Level 3                                                                                                                                                                | 0                                 | (10) |
| Balance, Ending, Assets                                                                                                                                                                 | 24                                | 35 |
| Unrealized gains (losses) on Level 3 assets and liabilities recognized in Net income (loss) in the period                                                                               | (7)                               | (4) |
| Unrealized gains (losses) on Level 3 assets and liabilities recognized in Other comprehensive income (loss) in the period                                                               | 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                                                                                                                                                       | 13                                | 14 |
| 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                                                                                                                                                       | 0                                 | 1 |
| 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 |
| 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                                                                                                                                                       | 20                                | 16 |
| 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                                                                                                                                                       | $ (7)                             | $ (3) |

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| - Definition
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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| - Definition
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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No definition available.
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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.
+ References
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| - Definition
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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| - Definition
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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| - Definition
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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| - Definition
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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| - Definition
Amount of transfer of financial instrument classified as an asset into level 3 of the fair value hierarchy.
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| - Definition
Amount of transfers of financial instrument classified as an asset out of level 3 of the fair value hierarchy.
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| - Definition
Fair value 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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| - Definition
Indicates line item in statement in which net income is reported that includes gain (loss) from asset measured at fair value using unobservable input (level 3).
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| - Definition
Indicates line item in statement in which other comprehensive income (OCI) is reported that includes gain (loss) from asset measured at fair value using unobservable input (level 3).
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