| **Investments (Net change in unrealized gains (losses) on investments) (Details) - USD ($) $ in Millions** | 12 Months Ended |
|------------------------------------------------------------------------------------------------------------|-----------------|
||
| **Schedule of Available-for-sale Securities [Line Items]**                                                 |            |   |   |
| Total net change in unrealized gains on investments                                                        | $ 758           | $ 224 | $ (1,119) |
| Fixed maturity securities                                                                                  |            |   |   |
| **Schedule of Available-for-sale Securities [Line Items]**                                                 |            |   |   |
| Total net change in unrealized gains on investments                                                        | 728             | 225 | (1,114) |
| Equity securities                                                                                          |            |   |   |
| **Schedule of Available-for-sale Securities [Line Items]**                                                 |            |   |   |
| Total net change in unrealized gains on investments                                                        | 32              | (2) | (6) |
| Other                                                                                                      |            |   |   |
| **Schedule of Available-for-sale Securities [Line Items]**                                                 |            |   |   |
| Total net change in unrealized gains on investments                                                        | $ (2)           | $ 1 | $ 1 |

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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=82897076&loc=d3e27357-111563
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| - Definition
Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.
+ References
No definition available.
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