| **Investments (Securities in a gross unrealized loss position by ratings) (Details) - USD ($) $ in Millions** | Sep. 30, 2024 | Dec. 31, 2023 |
|---------------------------------------------------------------------------------------------------------------|---------------|---------------|
| **Debt Securities, Available-for-sale [Line Items]**                                                          |          |          |
| Estimated Fair Value                                                                                          | $ 22,400      | $ 25,731      |
| Gross Unrealized Losses                                                                                       | 2,236         | 2,995         |
| U.S. Government, Government agencies and Government-sponsored enterprises                                     |          |          |
| **Debt Securities, Available-for-sale [Line Items]**                                                          |          |          |
| Estimated Fair Value                                                                                          | 2,127         | 2,273         |
| Gross Unrealized Losses                                                                                       | 265           | 309           |
| AAA                                                                                                           |          |          |
| **Debt Securities, Available-for-sale [Line Items]**                                                          |          |          |
| Estimated Fair Value                                                                                          | 1,277         | 1,524         |
| Gross Unrealized Losses                                                                                       | 221           | 261           |
| AA                                                                                                            |          |          |
| **Debt Securities, Available-for-sale [Line Items]**                                                          |          |          |
| Estimated Fair Value                                                                                          | 3,641         | 3,817         |
| Gross Unrealized Losses                                                                                       | 547           | 658           |
| A                                                                                                             |          |          |
| **Debt Securities, Available-for-sale [Line Items]**                                                          |          |          |
| Estimated Fair Value                                                                                          | 5,229         | 5,652         |
| Gross Unrealized Losses                                                                                       | 405           | 517           |
| BBB                                                                                                           |          |          |
| **Debt Securities, Available-for-sale [Line Items]**                                                          |          |          |
| Estimated Fair Value                                                                                          | 9,243         | 11,523        |
| Gross Unrealized Losses                                                                                       | 689           | 1,095         |
| Non-investment grade                                                                                          |          |          |
| **Debt Securities, Available-for-sale [Line Items]**                                                          |          |          |
| Estimated Fair Value                                                                                          | 883           | 942           |
| Gross Unrealized Losses                                                                                       | $ 109         | $ 155         |

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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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