| **Investments (Summary of fixed maturity and equity securities) (Details) - USD ($) $ in Millions** | Dec. 31, 2019 | Dec. 31, 2018 |
|-----------------------------------------------------------------------------------------------------|---------------|---------------|
| **Fixed maturity securities available-for-sale:**                                                   |          |          |
| Cost or Amortized Cost                                                                              | $ 38,106      | $ 38,081      |
| Gross Unrealized Gains                                                                              | 4,126         | 1,982         |
| Gross Unrealized Losses                                                                             | 45            | 521           |
| Estimated Fair Value                                                                                | 42,187        | 39,542        |
| **Total fixed maturity securities trading**                                                         |          |          |
| Debt securities, amortized cost                                                                     | 38,126        | 38,085        |
| Debt securities                                                                                     | 42,207        | 39,546        |
| Corporate and other bonds                                                                           |          |          |
| **Fixed maturity securities available-for-sale:**                                                   |          |          |
| Cost or Amortized Cost                                                                              | 19,789        | 18,764        |
| Gross Unrealized Gains                                                                              | 2,292         | 791           |
| Gross Unrealized Losses                                                                             | 32            | 395           |
| Estimated Fair Value                                                                                | 22,049        | 19,160        |
| **Total fixed maturity securities trading**                                                         |          |          |
| Debt securities                                                                                     | 22,728        | 19,814        |
| Unrealized OTTI Losses (Gains)                                                                      | 0             | 0             |
| States, municipalities and political subdivisions                                                   |          |          |
| **Fixed maturity securities available-for-sale:**                                                   |          |          |
| Cost or Amortized Cost                                                                              | 9,093         | 9,681         |
| Gross Unrealized Gains                                                                              | 1,559         | 1,076         |
| Gross Unrealized Losses                                                                             | 0             | 9             |
| Estimated Fair Value                                                                                | 10,652        | 10,748        |
| **Total fixed maturity securities trading**                                                         |          |          |
| Debt securities                                                                                     | 10,652        | 10,748        |
| Unrealized OTTI Losses (Gains)                                                                      | 0             | 0             |
| Residential mortgage-backed                                                                         |          |          |
| **Fixed maturity securities available-for-sale:**                                                   |          |          |
| Cost or Amortized Cost                                                                              | 4,387         | 4,815         |
| Gross Unrealized Gains                                                                              | 133           | 68            |
| Gross Unrealized Losses                                                                             | 1             | 57            |
| Estimated Fair Value                                                                                | 4,519         | 4,826         |
| **Total fixed maturity securities trading**                                                         |          |          |
| Unrealized OTTI Losses (Gains)                                                                      | (17)          | (20)          |
| Commercial mortgage-backed                                                                          |          |          |
| **Fixed maturity securities available-for-sale:**                                                   |          |          |
| Cost or Amortized Cost                                                                              | 2,265         | 2,200         |
| Gross Unrealized Gains                                                                              | 86            | 28            |
| Gross Unrealized Losses                                                                             | 5             | 32            |
| Estimated Fair Value                                                                                | 2,346         | 2,196         |
| **Total fixed maturity securities trading**                                                         |          |          |
| Unrealized OTTI Losses (Gains)                                                                      | 1             | 0             |
| Other asset-backed                                                                                  |          |          |
| **Fixed maturity securities available-for-sale:**                                                   |          |          |
| Cost or Amortized Cost                                                                              | 1,925         | 1,975         |
| Gross Unrealized Gains                                                                              | 41            | 11            |
| Gross Unrealized Losses                                                                             | 4             | 24            |
| Estimated Fair Value                                                                                | 1,962         | 1,962         |
| **Total fixed maturity securities trading**                                                         |          |          |
| Unrealized OTTI Losses (Gains)                                                                      | (3)           | 0             |
| Asset-backed                                                                                        |          |          |
| **Fixed maturity securities available-for-sale:**                                                   |          |          |
| Cost or Amortized Cost                                                                              | 8,577         | 8,990         |
| Gross Unrealized Gains                                                                              | 260           | 107           |
| Gross Unrealized Losses                                                                             | 10            | 113           |
| Estimated Fair Value                                                                                | 8,827         | 8,984         |
| **Total fixed maturity securities trading**                                                         |          |          |
| Debt securities                                                                                     | 8,827         | 8,984         |
| Unrealized OTTI Losses (Gains)                                                                      | (19)          | (20)          |
| U.S. Treasury and obligations of government-sponsored enterprises                                   |          |          |
| **Fixed maturity securities available-for-sale:**                                                   |          |          |
| Cost or Amortized Cost                                                                              | 146           | 156           |
| Gross Unrealized Gains                                                                              | 1             | 3             |
| Gross Unrealized Losses                                                                             | 2             | 0             |
| Estimated Fair Value                                                                                | 145           | 159           |
| **Total fixed maturity securities trading**                                                         |          |          |
| Unrealized OTTI Losses (Gains)                                                                      | 0             | 0             |
| Foreign government                                                                                  |          |          |
| **Fixed maturity securities available-for-sale:**                                                   |          |          |
| Cost or Amortized Cost                                                                              | 491           | 480           |
| Gross Unrealized Gains                                                                              | 14            | 5             |
| Gross Unrealized Losses                                                                             | 1             | 4             |
| Estimated Fair Value                                                                                | 504           | 481           |
| **Total fixed maturity securities trading**                                                         |          |          |
| Unrealized OTTI Losses (Gains)                                                                      | 0             | 0             |
| Redeemable preferred stock                                                                          |          |          |
| **Fixed maturity securities available-for-sale:**                                                   |          |          |
| Cost or Amortized Cost                                                                              | 10            | 10            |
| Gross Unrealized Gains                                                                              | 0             | 0             |
| Gross Unrealized Losses                                                                             | 0             | 0             |
| Estimated Fair Value                                                                                | 10            | 10            |
| **Total fixed maturity securities trading**                                                         |          |          |
| Unrealized OTTI Losses (Gains)                                                                      | 0             | 0             |
| Fixed maturity securities                                                                           |          |          |
| **Fixed maturity securities available-for-sale:**                                                   |          |          |
| Cost or Amortized Cost                                                                              | 38,106        | 38,081        |
| Gross Unrealized Gains                                                                              | 4,126         | 1,982         |
| Gross Unrealized Losses                                                                             | 45            | 521           |
| Estimated Fair Value                                                                                | 42,187        | 39,542        |
| **Total fixed maturity securities trading**                                                         |          |          |
| Unrealized OTTI Losses (Gains)                                                                      | (19)          | (20)          |
| Total fixed maturity securities trading                                                             |          |          |
| **Total fixed maturity securities trading**                                                         |          |          |
| Cost or amortized cost, trading securities                                                          | 20            | 4             |
| Estimated fair value, trading securities                                                            | $ 20          | $ 4           |

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