| **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                                                                                                                                                              | $ 454           | $ 407 |
| Reported in Net investment income                                                                                                                                                       | 0               |   |
| Total realized and unrealized investment gains (losses)                                                                                                                                 | (12)            | 9 |
| Total realized and unrealized investment gains (losses)                                                                                                                                 | (10)            | 18 |
| Purchases                                                                                                                                                                               | 279             | 126 |
| Sales                                                                                                                                                                                   | (77)            | (68) |
| Settlements                                                                                                                                                                             | (74)            | (102) |
| Transfers into Level 3                                                                                                                                                                  | 77              | 169 |
| Transfers out of Level 3                                                                                                                                                                | (212)           | (96) |
| Balance, Ending, Assets                                                                                                                                                                 | 437             | 454 |
| Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2018 recognized in Net income (loss)                                                                | (4)             |   |
| Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2018 recognized in Other comprehensive income (loss)                                                | (9)             |   |
| Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2017 recognized in Net income (loss)                                                                |            | 0 |
| Corporate and other bonds                                                                                                                                                               |            |   |
| **Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]**                                                                       |            |   |
| Balance, Beginning, Assets                                                                                                                                                              | 98              | 130 |
| Reported in Net investment income                                                                                                                                                       | 0               |   |
| Total realized and unrealized investment gains (losses)                                                                                                                                 | (4)             | 3 |
| Total realized and unrealized investment gains (losses)                                                                                                                                 | (5)             | 3 |
| Purchases                                                                                                                                                                               | 117             | 18 |
| Sales                                                                                                                                                                                   | (5)             | (5) |
| Settlements                                                                                                                                                                             | (9)             | (54) |
| Transfers into Level 3                                                                                                                                                                  | 35              | 16 |
| Transfers out of Level 3                                                                                                                                                                | (9)             | (10) |
| Balance, Ending, Assets                                                                                                                                                                 | 222             | 98 |
| Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2018 recognized in Net income (loss)                                                                | 0               |   |
| Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2018 recognized in Other comprehensive income (loss)                                                | (5)             |   |
| Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2017 recognized in Net income (loss)                                                                |            | 0 |
| States, municipalities and political subdivisions                                                                                                                                       |            |   |
| **Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]**                                                                       |            |   |
| Balance, Beginning, Assets                                                                                                                                                              | 1               | 1 |
| Reported in Net investment income                                                                                                                                                       | 0               |   |
| Total realized and unrealized investment gains (losses)                                                                                                                                 | 0               | 0 |
| Total realized and unrealized investment gains (losses)                                                                                                                                 | 0               | 0 |
| Purchases                                                                                                                                                                               | 0               | 0 |
| Sales                                                                                                                                                                                   | 0               | 0 |
| Settlements                                                                                                                                                                             | (1)             | 0 |
| Transfers into Level 3                                                                                                                                                                  | 0               | 0 |
| Transfers out of Level 3                                                                                                                                                                | 0               | 0 |
| Balance, Ending, Assets                                                                                                                                                                 | 0               | 1 |
| Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2018 recognized in Net income (loss)                                                                | 0               |   |
| Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2018 recognized in Other comprehensive income (loss)                                                | 0               |   |
| Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2017 recognized in Net income (loss)                                                                |            | 0 |
| Asset-backed                                                                                                                                                                            |            |   |
| **Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]**                                                                       |            |   |
| Balance, Beginning, Assets                                                                                                                                                              | 335             | 199 |
| Reported in Net investment income                                                                                                                                                       | 0               |   |
| Total realized and unrealized investment gains (losses)                                                                                                                                 | (8)             | 3 |
| Total realized and unrealized investment gains (losses)                                                                                                                                 | (3)             | 5 |
| Purchases                                                                                                                                                                               | 162             | 107 |
| Sales                                                                                                                                                                                   | (72)            | 0 |
| Settlements                                                                                                                                                                             | (64)            | (43) |
| Transfers into Level 3                                                                                                                                                                  | 42              | 153 |
| Transfers out of Level 3                                                                                                                                                                | (203)           | (86) |
| Balance, Ending, Assets                                                                                                                                                                 | 197             | 335 |
| Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2018 recognized in Net income (loss)                                                                | (2)             |   |
| Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2018 recognized in Other comprehensive income (loss)                                                | (4)             |   |
| Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2017 recognized in Net income (loss)                                                                |            | 0 |
| Equity securities                                                                                                                                                                       |            |   |
| **Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]**                                                                       |            |   |
| Balance, Beginning, Assets                                                                                                                                                              | 20              | 19 |
| Reported in Net investment income                                                                                                                                                       | 0               |   |
| Total realized and unrealized investment gains (losses)                                                                                                                                 | 0               | 3 |
| Total realized and unrealized investment gains (losses)                                                                                                                                 | (2)             | 3 |
| Purchases                                                                                                                                                                               | 0               | 1 |
| Sales                                                                                                                                                                                   | 0               | (3) |
| Settlements                                                                                                                                                                             | 0               | 0 |
| Transfers into Level 3                                                                                                                                                                  | 0               | 0 |
| Transfers out of Level 3                                                                                                                                                                | 0               | 0 |
| Balance, Ending, Assets                                                                                                                                                                 | 18              | 20 |
| Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2018 recognized in Net income (loss)                                                                | (2)             |   |
| Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2018 recognized in Other comprehensive income (loss)                                                | 0               |   |
| Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2017 recognized in Net income (loss)                                                                |            | 0 |
| Derivative financial instruments                                                                                                                                                        |            |   |
| **Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]**                                                                       |            |   |
| Balance, Beginning, Assets                                                                                                                                                              | 0               | 0 |
| Reported in Net investment income                                                                                                                                                       | 0               |   |
| Total realized and unrealized investment gains (losses)                                                                                                                                 | 0               | 0 |
| Total realized and unrealized investment gains (losses)                                                                                                                                 | 0               | 1 |
| Purchases                                                                                                                                                                               | 0               | 0 |
| Sales                                                                                                                                                                                   | 0               | (1) |
| Settlements                                                                                                                                                                             | 0               | 0 |
| Transfers into Level 3                                                                                                                                                                  | 0               | 0 |
| Transfers out of Level 3                                                                                                                                                                | 0               | 0 |
| Balance, Ending, Assets                                                                                                                                                                 | 0               | 0 |
| Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2018 recognized in Net income (loss)                                                                | 0               |   |
| Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2018 recognized in Other comprehensive income (loss)                                                | 0               |   |
| Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2017 recognized in Net income (loss)                                                                |            | 0 |
| Life settlement contracts, included in Other assets                                                                                                                                     |            |   |
| **Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]**                                                                       |            |   |
| Balance, Beginning, Assets                                                                                                                                                              | 0               | 58 |
| Total realized and unrealized investment gains (losses)                                                                                                                                 |            | 0 |
| Total realized and unrealized investment gains (losses)                                                                                                                                 |            | 6 |
| Purchases                                                                                                                                                                               |            | 0 |
| Sales                                                                                                                                                                                   |            | (59) |
| Settlements                                                                                                                                                                             |            | (5) |
| Transfers into Level 3                                                                                                                                                                  |            | 0 |
| Transfers out of Level 3                                                                                                                                                                |            | 0 |
| Balance, Ending, Assets                                                                                                                                                                 |            | 0 |
| Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2017 recognized in Net income (loss)                                                                |            | 0 |
| Reported in Net realized investment gains (losses)                                                                                                                                      |            |   |
| **Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]**                                                                       |            |   |
| Reported in Other comprehensive income (loss)                                                                                                                                           | 2               | 3 |
| Reported in Net realized investment gains (losses) | Corporate and other bonds                                                                                                          |            |   |
| **Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]**                                                                       |            |   |
| Reported in Other comprehensive income (loss)                                                                                                                                           | (1)             | 0 |
| Reported in Net realized investment gains (losses) | States, municipalities and political subdivisions                                                                                  |            |   |
| **Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]**                                                                       |            |   |
| Reported in Other comprehensive income (loss)                                                                                                                                           | 0               | 0 |
| Reported in Net realized investment gains (losses) | Asset-backed                                                                                                                       |            |   |
| **Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]**                                                                       |            |   |
| Reported in Other comprehensive income (loss)                                                                                                                                           | 5               | 2 |
| Reported in Net realized investment gains (losses) | Equity securities                                                                                                                  |            |   |
| **Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]**                                                                       |            |   |
| Reported in Other comprehensive income (loss)                                                                                                                                           | (2)             | 0 |
| Reported in Net realized investment gains (losses) | Derivative financial instruments                                                                                                   |            |   |
| **Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]**                                                                       |            |   |
| Reported in Other comprehensive income (loss)                                                                                                                                           | $ 0             | 1 |
| Reported in Net realized investment gains (losses) | Life settlement contracts, included in Other assets                                                                                |            |   |
| **Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]**                                                                       |            |   |
| Reported in Other comprehensive income (loss)                                                                                                                                           |            | 0 |
| Reported in Other revenues                                                                                                                                                              |            |   |
| **Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]**                                                                       |            |   |
| Reported in Other comprehensive income (loss)                                                                                                                                           |            | 6 |
| Reported in Other revenues | Corporate and other bonds                                                                                                                                  |            |   |
| **Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]**                                                                       |            |   |
| Reported in Other comprehensive income (loss)                                                                                                                                           |            | 0 |
| Reported in Other revenues | States, municipalities and political subdivisions                                                                                                          |            |   |
| **Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]**                                                                       |            |   |
| Reported in Other comprehensive income (loss)                                                                                                                                           |            | 0 |
| Reported in Other revenues | Asset-backed                                                                                                                                               |            |   |
| **Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]**                                                                       |            |   |
| Reported in Other comprehensive income (loss)                                                                                                                                           |            | 0 |
| Reported in Other revenues | Equity securities                                                                                                                                          |            |   |
| **Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]**                                                                       |            |   |
| Reported in Other comprehensive income (loss)                                                                                                                                           |            | 0 |
| Reported in Other revenues | Derivative financial instruments                                                                                                                           |            |   |
| **Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]**                                                                       |            |   |
| Reported in Other comprehensive income (loss)                                                                                                                                           |            | 0 |
| Reported in Other revenues | Life settlement contracts, included in Other assets                                                                                                        |            |   |
| **Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]**                                                                       |            |   |
| Reported in Other comprehensive income (loss)                                                                                                                                           |            | $ 6 |

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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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Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Net Investment Income
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Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Unrealized Gain (Loss) Included in Earnings
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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 (holding) gain (loss) which is included in the statement of income (or changes in net assets) related to those assets still held at the reporting date for which fair value is measured on a recurring basis using significant unobservable inputs (Level 3).
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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 the income statement for 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 gain (loss) recognized in other comprehensive income (loss) for 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 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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