| **Claim and Claim Adjustment Expense Reserves (Net prior year claim and claim adjustment expense reserve development) (Details) (USD $)In Millions, unless otherwise specified** | 12 Months Ended |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|-----------------|
||
| Increase (decrease) in provision for insured events of prior years                                                                                                               | $ (115)         | $ (182) | $ (429) |
| Property and casualty reserve development [Member]                                                                                                                               |            |   |   |
| Increase (decrease) in provision for insured events of prior years                                                                                                               | (115)           | (180) | (429) |
| Life reserve development in life company [Member]                                                                                                                                |            |   |   |
| Increase (decrease) in provision for insured events of prior years                                                                                                               |       | $ (2) |    |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of provision in the period for claims incurred in prior reporting periods and related claims settlement costs.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Financial Reporting Release (FRR) -Number 403 -Paragraph 04 -Subparagraph bReference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6482485&loc=d3e14764-158437
+ Details**Name:**us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaimsPriorYears**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**duration |