| **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                                                                                                               | $ (429)         | $ (544) | $ (240) |
| Core (Non-A&EP) [Member]                                                                                                                                                     |            |   |   |
| Increase (decrease) in provision for insured events of prior years                                                                                                               | (429)           | (545) | (396) |
| A&EP [Member]                                                                                                                                                                |            |   |   |
| Increase (decrease) in provision for insured events of prior years                                                                                                               |       |    | 155 |
| Property and casualty reserve development [Member]                                                                                                                               |            |   |   |
| Increase (decrease) in provision for insured events of prior years                                                                                                               | (429)           | (545) | (241) |
| Life reserve development in life company [Member]                                                                                                                                |            |   |   |
| Increase (decrease) in provision for insured events of prior years                                                                                                               |       | $ 1 | $ 1 |

| 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 AICPA -Name Statement of Position (SOP) -Number 94-5 -Paragraph 11 -Subparagraph b -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.  This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Financial Reporting Release (FRR) -Number 403 -Paragraph 04 -Subparagraph bReference 3: 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 |