| **Investments (Summary of fixed maturity and equity securities) (Details) - USD ($) $ in Millions** | Sep. 30, 2020 | Jun. 30, 2020 | Dec. 31, 2019 |
|-----------------------------------------------------------------------------------------------------|---------------|---------------|---------------|
| **Fixed maturity securities available-for-sale:**                                                   |          |          |          |
| Cost or Amortized Cost                                                                              | $ 38,962      |          | $ 38,106      |
| Gross Unrealized Gains                                                                              | 5,160         |          | 4,126         |
| Gross Unrealized Losses                                                                             | 181           |          | 45            |
| Estimated Fair Value                                                                                | 43,894        |          | 42,187        |
| **Total fixed maturity securities trading**                                                         |          |          |          |
| Debt securities, amortized cost                                                                     | 38,969        |          | 38,126        |
| Debt securities                                                                                     | 43,901        |          | 42,207        |
| Allowance for Credit Losses                                                                         | 47            | $ 51          | 0             |
| Corporate and other bonds                                                                           |          |          |          |
| **Fixed maturity securities available-for-sale:**                                                   |          |          |          |
| Cost or Amortized Cost                                                                              | 20,734        |          | 19,789        |
| Gross Unrealized Gains                                                                              | 3,047         |          | 2,292         |
| Gross Unrealized Losses                                                                             | 89            |          | 32            |
| Estimated Fair Value                                                                                | 23,658        |          | 22,049        |
| Unrealized OTTI Losses (Gains)                                                                      |          |          | 0             |
| **Total fixed maturity securities trading**                                                         |          |          |          |
| Debt securities                                                                                     | 24,525        |          | 22,728        |
| Allowance for Credit Losses                                                                         | 34            | 39            | 0             |
| Asset-backed                                                                                        |          |          |          |
| **Fixed maturity securities available-for-sale:**                                                   |          |          |          |
| Cost or Amortized Cost                                                                              | 7,941         |          | 8,577         |
| Gross Unrealized Gains                                                                              | 314           |          | 260           |
| Gross Unrealized Losses                                                                             | 90            |          | 10            |
| Estimated Fair Value                                                                                | 8,152         |          | 8,827         |
| Unrealized OTTI Losses (Gains)                                                                      |          |          | (19)          |
| **Total fixed maturity securities trading**                                                         |          |          |          |
| Debt securities                                                                                     | 8,152         |          | 8,827         |
| Allowance for Credit Losses                                                                         | 13            | $ 12          | 0             |
| States, municipalities and political subdivisions                                                   |          |          |          |
| **Fixed maturity securities available-for-sale:**                                                   |          |          |          |
| Cost or Amortized Cost                                                                              | 9,459         |          | 9,093         |
| Gross Unrealized Gains                                                                              | 1,766         |          | 1,559         |
| Gross Unrealized Losses                                                                             | 1             |          | 0             |
| Estimated Fair Value                                                                                | 11,224        |          | 10,652        |
| Unrealized OTTI Losses (Gains)                                                                      |          |          | 0             |
| **Total fixed maturity securities trading**                                                         |          |          |          |
| Debt securities                                                                                     | 11,224        |          | 10,652        |
| Allowance for Credit Losses                                                                         | 0             |          |          |
| Residential mortgage-backed                                                                         |          |          |          |
| **Fixed maturity securities available-for-sale:**                                                   |          |          |          |
| Cost or Amortized Cost                                                                              | 3,796         |          | 4,387         |
| Gross Unrealized Gains                                                                              | 153           |          | 133           |
| Gross Unrealized Losses                                                                             | 1             |          | 1             |
| Estimated Fair Value                                                                                | 3,948         |          | 4,519         |
| Unrealized OTTI Losses (Gains)                                                                      |          |          | (17)          |
| **Total fixed maturity securities trading**                                                         |          |          |          |
| Allowance for Credit Losses                                                                         | 0             |          |          |
| Commercial mortgage-backed                                                                          |          |          |          |
| **Fixed maturity securities available-for-sale:**                                                   |          |          |          |
| Cost or Amortized Cost                                                                              | 2,048         |          | 2,265         |
| Gross Unrealized Gains                                                                              | 85            |          | 86            |
| Gross Unrealized Losses                                                                             | 70            |          | 5             |
| Estimated Fair Value                                                                                | 2,050         |          | 2,346         |
| Unrealized OTTI Losses (Gains)                                                                      |          |          | 1             |
| **Total fixed maturity securities trading**                                                         |          |          |          |
| Allowance for Credit Losses                                                                         | 13            |          |          |
| Other asset-backed                                                                                  |          |          |          |
| **Fixed maturity securities available-for-sale:**                                                   |          |          |          |
| Cost or Amortized Cost                                                                              | 2,097         |          | 1,925         |
| Gross Unrealized Gains                                                                              | 76            |          | 41            |
| Gross Unrealized Losses                                                                             | 19            |          | 4             |
| Estimated Fair Value                                                                                | 2,154         |          | 1,962         |
| Unrealized OTTI Losses (Gains)                                                                      |          |          | (3)           |
| **Total fixed maturity securities trading**                                                         |          |          |          |
| Allowance for Credit Losses                                                                         | 0             |          |          |
| U.S. Treasury and obligations of government-sponsored enterprises                                   |          |          |          |
| **Fixed maturity securities available-for-sale:**                                                   |          |          |          |
| Cost or Amortized Cost                                                                              | 347           |          | 146           |
| Gross Unrealized Gains                                                                              | 4             |          | 1             |
| Gross Unrealized Losses                                                                             | 1             |          | 2             |
| Estimated Fair Value                                                                                | 350           |          | 145           |
| Unrealized OTTI Losses (Gains)                                                                      |          |          | 0             |
| **Total fixed maturity securities trading**                                                         |          |          |          |
| Allowance for Credit Losses                                                                         | 0             |          |          |
| Foreign government                                                                                  |          |          |          |
| **Fixed maturity securities available-for-sale:**                                                   |          |          |          |
| Cost or Amortized Cost                                                                              | 481           |          | 491           |
| Gross Unrealized Gains                                                                              | 29            |          | 14            |
| Gross Unrealized Losses                                                                             | 0             |          | 1             |
| Estimated Fair Value                                                                                | 510           |          | 504           |
| Unrealized OTTI Losses (Gains)                                                                      |          |          | 0             |
| **Total fixed maturity securities trading**                                                         |          |          |          |
| Allowance for Credit Losses                                                                         | 0             |          |          |
| Redeemable preferred stock                                                                          |          |          |          |
| **Fixed maturity securities available-for-sale:**                                                   |          |          |          |
| Cost or Amortized Cost                                                                              | 0             |          | 10            |
| Gross Unrealized Gains                                                                              | 0             |          | 0             |
| Gross Unrealized Losses                                                                             | 0             |          | 0             |
| Estimated Fair Value                                                                                | 0             |          | 10            |
| Unrealized OTTI Losses (Gains)                                                                      |          |          | 0             |
| **Total fixed maturity securities trading**                                                         |          |          |          |
| Allowance for Credit Losses                                                                         | 0             |          |          |
| Fixed maturity securities                                                                           |          |          |          |
| **Fixed maturity securities available-for-sale:**                                                   |          |          |          |
| Cost or Amortized Cost                                                                              | 38,962        |          | 38,106        |
| Gross Unrealized Gains                                                                              | 5,160         |          | 4,126         |
| Gross Unrealized Losses                                                                             | 181           |          | 45            |
| Estimated Fair Value                                                                                | 43,894        |          | 42,187        |
| Unrealized OTTI Losses (Gains)                                                                      |          |          | (19)          |
| **Total fixed maturity securities trading**                                                         |          |          |          |
| Allowance for Credit Losses                                                                         | 47            |          |          |
| Total fixed maturity securities trading                                                             |          |          |          |
| **Total fixed maturity securities trading**                                                         |          |          |          |
| Cost or amortized cost, trading securities                                                          | 7             |          | 20            |
| Estimated fair value, trading securities                                                            | $ 7           |          | $ 20          |

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