| **Investments (Securities in a gross unrealized loss position by ratings) (Details) - USD ($) $ in Millions** | Sep. 30, 2023 | Dec. 31, 2022 |
|---------------------------------------------------------------------------------------------------------------|---------------|---------------|
| **Debt Securities, Available-for-sale [Line Items]**                                                          |          |          |
| Estimated Fair Value                                                                                          | $ 31,117      | $ 29,511      |
| Gross Unrealized Losses                                                                                       | 4,888         | 4,056         |
| U.S. Government, Government agencies and Government-sponsored enterprises                                     |          |          |
| **Debt Securities, Available-for-sale [Line Items]**                                                          |          |          |
| Estimated Fair Value                                                                                          | 2,620         | 2,355         |
| Gross Unrealized Losses                                                                                       | 466           | 337           |
| AAA                                                                                                           |          |          |
| **Debt Securities, Available-for-sale [Line Items]**                                                          |          |          |
| Estimated Fair Value                                                                                          | 1,893         | 1,559         |
| Gross Unrealized Losses                                                                                       | 382           | 298           |
| AA                                                                                                            |          |          |
| **Debt Securities, Available-for-sale [Line Items]**                                                          |          |          |
| Estimated Fair Value                                                                                          | 4,458         | 4,327         |
| Gross Unrealized Losses                                                                                       | 1,037         | 817           |
| A                                                                                                             |          |          |
| **Debt Securities, Available-for-sale [Line Items]**                                                          |          |          |
| Estimated Fair Value                                                                                          | 7,240         | 6,615         |
| Gross Unrealized Losses                                                                                       | 913           | 749           |
| BBB                                                                                                           |          |          |
| **Debt Securities, Available-for-sale [Line Items]**                                                          |          |          |
| Estimated Fair Value                                                                                          | 13,704        | 13,226        |
| Gross Unrealized Losses                                                                                       | 1,881         | 1,621         |
| Non-investment grade                                                                                          |          |          |
| **Debt Securities, Available-for-sale [Line Items]**                                                          |          |          |
| Estimated Fair Value                                                                                          | 1,202         | 1,429         |
| Gross Unrealized Losses                                                                                       | $ 209         | $ 234         |

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| - Definition
Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position without allowance for credit loss.
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Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position, without allowance for credit loss. Includes beneficial interest in securitized financial asset.
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