| **Investments - (Narrative) (Details) $ in Millions**                                                             | 3 Months Ended |          |
|-------------------------------------------------------------------------------------------------------------------|----------------|----------|
||
| **Investments [Abstract]**                                                                                        |           |     |
| Equity Securities at Fair Value                                                                                   | $ 11,557       | $ 10,989 |
| Fair value of largest single common stock holding                                                                 | $ 942          | $ 842    |
| Largest equity holdings to total equity portfolio                                                                 | 8.40%          | 7.90%    |
| Largest equity holdings to total investment portfolio                                                             | 3.70%          | 3.40%    |
| Allowance for credit loss on fixed-maturity                                                                       | $ 27           | $ 18     |
| Number of fixed-maturity securities in a total unrealized loss position | security                                | 3,329          | 2,840    |
| Fixed-maturity securities, total unrealized loss                                                                  | $ 714          | $ 687    |
| Number of fixed-maturity securities in continuous unrealized loss position and below 70 percent of amortized cost | 12             | 20       |
| Fixed maturity investments, Percentage of amortized costs                                                         | 70.00%         |     |

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Amount of unrealized loss on securities classified as available-for-sale.
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Fixed maturity investments, Percentage of amortized costs.
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| X                                                                                                                                                                                                                                                        |
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| - Definition
Largest Single Common Stock Holding
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largest equity holdings to total equity portfolio
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Largest equity holdings to total portfolio
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| X                                                                                                                                                                                                                                                                                            |
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Number Of Securities Continuous Unrealized Loss Position
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| - Definition
Number Of Securities Continuous Unrealized Loss Position and Below 70 Percent of Amortized Cost
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| - Definition
Amount of allowance for credit loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).
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| - Definition
Amount of investment in marketable security.
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