| **Investments (Net change in unrealized gains (losses) on investments) (Details) (USD $)In Millions, unless otherwise specified** | 12 Months Ended |
|-----------------------------------------------------------------------------------------------------------------------------------|-----------------|
||
| Net change in unrealized gains (losses) on investments                                                                            | $ (2,556)       | $ 1,875 | $ 1,437 |
| Fixed maturity securities [Member]                                                                                                |            |   |   |
| Net change in unrealized gains (losses) on investments                                                                            | (2,541)         | 1,871 | 1,442 |
| Equity securities [Member]                                                                                                        |            |   |   |
| Net change in unrealized gains (losses) on investments                                                                            | (15)            | 5 | (2) |
| Other [Member]                                                                                                                    |            |   |   |
| Net change in unrealized gains (losses) on investments                                                                            |       | $ (1) | $ (3) |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - 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
+ Details**Name:**us-gaap_AvailableForSaleSecuritiesChangeInNetUnrealizedHoldingGainLoss**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**duration |