| **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                                                                                                                                                              | $ 2,014                           | $ 1,676 |
| Reported in Net investment gains (losses)                                                                                                                                               | $ (13)                            | $ (4) |
| Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]                                | Net investment losses             | Net investment losses |
| 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)                                                                                                                                           | $ (29)                            | $ 48 |
| Total realized and unrealized investment gains (losses)                                                                                                                                 | (9)                               | 57 |
| Purchases                                                                                                                                                                               | 480                               | 467 |
| Sales                                                                                                                                                                                   | (43)                              | (4) |
| Settlements                                                                                                                                                                             | (187)                             | (97) |
| Transfers into Level 3                                                                                                                                                                  | 11                                | 34 |
| Transfers out of Level 3                                                                                                                                                                | (50)                              | (119) |
| Balance, Ending, Assets                                                                                                                                                                 | 2,216                             | 2,014 |
| Unrealized gains (losses) on Level 3 assets and liabilities recognized in Net income (loss) in the period                                                                               | 7                                 | (7) |
| Unrealized gains (losses) on Level 3 assets and liabilities recognized in Other comprehensive income (loss) in the period                                                               | (35)                              | 48 |
| Corporate and other bonds                                                                                                                                                               |                              |   |
| **Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]**                                                                       |                              |   |
| Balance, Beginning, Assets                                                                                                                                                              | 1,045                             | 810 |
| Reported in Net investment gains (losses)                                                                                                                                               | (1)                               | 0 |
| Reported in Other comprehensive income (loss)                                                                                                                                           | (15)                              | 38 |
| Total realized and unrealized investment gains (losses)                                                                                                                                 | (16)                              | 38 |
| Purchases                                                                                                                                                                               | 352                               | 219 |
| Sales                                                                                                                                                                                   | (10)                              | 0 |
| Settlements                                                                                                                                                                             | (104)                             | (33) |
| Transfers into Level 3                                                                                                                                                                  | 11                                | 11 |
| Transfers out of Level 3                                                                                                                                                                | 0                                 | 0 |
| Balance, Ending, Assets                                                                                                                                                                 | 1,278                             | 1,045 |
| Unrealized gains (losses) on Level 3 assets and liabilities recognized in Net income (loss) in the period                                                                               | (1)                               | 0 |
| Unrealized gains (losses) on Level 3 assets and liabilities recognized in Other comprehensive income (loss) in the period                                                               | (21)                              | 38 |
| States, municipalities and political subdivisions                                                                                                                                       |                              |   |
| **Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]**                                                                       |                              |   |
| Balance, Beginning, Assets                                                                                                                                                              | 44                                | 43 |
| Reported in Net investment gains (losses)                                                                                                                                               | 0                                 | 0 |
| Reported in Other comprehensive income (loss)                                                                                                                                           | (2)                               | 1 |
| Total realized and unrealized investment gains (losses)                                                                                                                                 | (2)                               | 1 |
| 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                                                                                                                                                                 | 42                                | 44 |
| 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                                                               | (2)                               | 1 |
| Asset-backed                                                                                                                                                                            |                              |   |
| **Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]**                                                                       |                              |   |
| Balance, Beginning, Assets                                                                                                                                                              | 901                               | 788 |
| Reported in Net investment gains (losses)                                                                                                                                               | (12)                              | (4) |
| Reported in Other comprehensive income (loss)                                                                                                                                           | (12)                              | 9 |
| Total realized and unrealized investment gains (losses)                                                                                                                                 | (3)                               | 25 |
| Purchases                                                                                                                                                                               | 125                               | 248 |
| Sales                                                                                                                                                                                   | (14)                              | 0 |
| Settlements                                                                                                                                                                             | (83)                              | (64) |
| Transfers into Level 3                                                                                                                                                                  | 0                                 | 23 |
| Transfers out of Level 3                                                                                                                                                                | (50)                              | (119) |
| Balance, Ending, Assets                                                                                                                                                                 | 876                               | 901 |
| 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                                                               | (12)                              | 9 |
| Equity securities                                                                                                                                                                       |                              |   |
| **Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]**                                                                       |                              |   |
| Balance, Beginning, Assets                                                                                                                                                              | 24                                | 35 |
| Reported in Net investment gains (losses)                                                                                                                                               | 0                                 | 0 |
| Reported in Other comprehensive income (loss)                                                                                                                                           | 0                                 | 0 |
| Total realized and unrealized investment gains (losses)                                                                                                                                 | 12                                | (7) |
| Purchases                                                                                                                                                                               | 3                                 | 0 |
| Sales                                                                                                                                                                                   | (19)                              | (4) |
| Settlements                                                                                                                                                                             | 0                                 | 0 |
| Transfers into Level 3                                                                                                                                                                  | 0                                 | 0 |
| Transfers out of Level 3                                                                                                                                                                | 0                                 | 0 |
| Balance, Ending, Assets                                                                                                                                                                 | 20                                | 24 |
| Unrealized gains (losses) on Level 3 assets and liabilities recognized in Net income (loss) in the period                                                                               | 8                                 | (7) |
| 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                                                                                                                                                       | 33                                | 13 |
| 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                                 | 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 |
| 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                                                                                                                                                       | 21                                | 20 |
| 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                                                                                                                                                       | $ 12                              | $ (7) |

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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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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.
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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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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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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 of income or comprehensive income that includes gain (loss) from asset measured at fair value using unobservable input (level 3).
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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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