| **Investments (Net change in unrealized gains (losses) on investments) (Details) - USD ($) $ in Millions** | 12 Months Ended |
|------------------------------------------------------------------------------------------------------------|-----------------|
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| Net change in unrealized gains (losses) on investments                                                     | $ (1,119)       | $ 1,517 | $ (2,556) |
| Fixed maturity securities [Member]                                                                         |            |   |   |
| Net change in unrealized gains (losses) on investments                                                     | (1,114)         | 1,511 | (2,541) |
| Total equity securities available-for-sale [Member]                                                        |            |   |   |
| Net change in unrealized gains (losses) on investments                                                     | (6)             | 6 | (15) |
| Other [Member]                                                                                             |            |   |   |
| Net change in unrealized gains (losses) on investments                                                     | $ 1             | $ 0 | $ 0 |

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| - Definition
This item represents the pretax change in net unrealized holding gain (loss) on available-for-sale securities that has been included in accumulated other comprehensive income, a separate component of shareholders' equity, during the period.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 9 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27357-111563
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