| **Investments (Components of other-than-temporary impairment losses recognized in earnings) (Details) - USD ($) $ in Millions** | 3 Months Ended | 9 Months Ended |
|---------------------------------------------------------------------------------------------------------------------------------|----------------|----------------|
||
| **Debt Securities, Available-for-sale [Line Items]**                                                                            |           |           |   |   |
| Impairment losses (gains) recognized in earnings                                                                                | $ 12           | $ 12           | $ 32 | $ 37 |
| Corporate and other bonds                                                                                                       |           |           |   |   |
| **Debt Securities, Available-for-sale [Line Items]**                                                                            |           |           |   |   |
| Impairment losses (gains) recognized in earnings                                                                                | 8              | 8              | 23 | 25 |
| Asset-backed                                                                                                                    |           |           |   |   |
| **Debt Securities, Available-for-sale [Line Items]**                                                                            |           |           |   |   |
| Impairment losses (gains) recognized in earnings                                                                                | $ 4            | $ 4            | $ 9 | $ 12 |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of other-than-temporary impairment (OTTI) on investment in debt security, recognized in earnings.
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| X                                                                                                                                                           |
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