| **Investments (Components of other-than-temporary impairment losses recognized in earnings) (Details) (USD $)In Millions, unless otherwise specified** | 12 Months Ended                                                                                                                                                                                          |
|--------------------------------------------------------------------------------------------------------------------------------------------------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
||
| Other-than-temporary impairment losses recognized in earnings                                                                                          | $ 77us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionRecognizedInEarningsNet                                                                                                                  | $ 76us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionRecognizedInEarningsNet | $ 150us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionRecognizedInEarningsNet |
| Corporate and other bonds [Member]                                                                                                                     |                                                                                                                                                                                                     |   |   |
| Other-than-temporary impairment losses recognized in earnings                                                                                          | 18us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionRecognizedInEarningsNet/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_CorporateDebtSecuritiesMember                            | 20us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionRecognizedInEarningsNet/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_CorporateDebtSecuritiesMember | 25us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionRecognizedInEarningsNet/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_CorporateDebtSecuritiesMember |
| States, municipalities and political subdivisions [Member]                                                                                             |                                                                                                                                                                                                     |   |   |
| Other-than-temporary impairment losses recognized in earnings                                                                                          | 46us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionRecognizedInEarningsNet/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_USStatesAndPoliticalSubdivisionsMember                   |   | 34us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionRecognizedInEarningsNet/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_USStatesAndPoliticalSubdivisionsMember |
| Residential mortgage-backed [Member]                                                                                                                   |                                                                                                                                                                                                     |   |   |
| Other-than-temporary impairment losses recognized in earnings                                                                                          | 5us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionRecognizedInEarningsNet/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_ResidentialMortgageBackedSecuritiesMember                 | 19us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionRecognizedInEarningsNet/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_ResidentialMortgageBackedSecuritiesMember | 48us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionRecognizedInEarningsNet/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_ResidentialMortgageBackedSecuritiesMember |
| Other asset-backed [Member]                                                                                                                            |                                                                                                                                                                                                     |   |   |
| Other-than-temporary impairment losses recognized in earnings                                                                                          | 1us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionRecognizedInEarningsNet/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_AssetBackedSecuritiesSecuritizedLoansAndReceivablesMember | 2us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionRecognizedInEarningsNet/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_AssetBackedSecuritiesSecuritizedLoansAndReceivablesMember |   |
| Total asset-backed [Member]                                                                                                                            |                                                                                                                                                                                                     |   |   |
| Other-than-temporary impairment losses recognized in earnings                                                                                          | 6us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionRecognizedInEarningsNet/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_AssetBackedSecuritiesMember                               | 21us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionRecognizedInEarningsNet/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_AssetBackedSecuritiesMember | 48us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionRecognizedInEarningsNet/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_AssetBackedSecuritiesMember |
| U.S. Treasury and obligations of government-sponsored enterprises [Member]                                                                             |                                                                                                                                                                                                     |   |   |
| Other-than-temporary impairment losses recognized in earnings                                                                                          |                                                                                                                                                                                                     |   | 1us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionRecognizedInEarningsNet/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_USTreasuryAndGovernmentMember |
| Total fixed maturity securities available-for-sale [Member]                                                                                            |                                                                                                                                                                                                     |   |   |
| Other-than-temporary impairment losses recognized in earnings                                                                                          | 70us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionRecognizedInEarningsNet/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_FixedIncomeSecuritiesMember                              | 41us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionRecognizedInEarningsNet/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_FixedIncomeSecuritiesMember | 108us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionRecognizedInEarningsNet/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_FixedIncomeSecuritiesMember |
| Common stock [Member]                                                                                                                                  |                                                                                                                                                                                                     |   |   |
| Other-than-temporary impairment losses recognized in earnings                                                                                          | 7us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionRecognizedInEarningsNet/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_CommonStockMember                                         | 8us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionRecognizedInEarningsNet/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_CommonStockMember | 6us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionRecognizedInEarningsNet/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_CommonStockMember |
| Preferred stock [Member]                                                                                                                               |                                                                                                                                                                                                     |   |   |
| Other-than-temporary impairment losses recognized in earnings                                                                                          |                                                                                                                                                                                                     | 26us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionRecognizedInEarningsNet/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_PreferredStockMember | 36us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionRecognizedInEarningsNet/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_PreferredStockMember |
| Total equity securities available-for-sale [Member]                                                                                                    |                                                                                                                                                                                                     |   |   |
| Other-than-temporary impairment losses recognized in earnings                                                                                          | 7us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionRecognizedInEarningsNet/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_EquitySecuritiesMember                                    | 34us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionRecognizedInEarningsNet/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_EquitySecuritiesMember | 42us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionRecognizedInEarningsNet/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_EquitySecuritiesMember |
| Short term investments [Member]                                                                                                                        |                                                                                                                                                                                                     |   |   |
| Other-than-temporary impairment losses recognized in earnings                                                                                          |                                                                                                                                                                                                     | $ 1us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionRecognizedInEarningsNet/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_ShortTermInvestmentsMember |   |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The amount of other than temporary impairment (OTTI) losses on equity securities, OTTI related to credit losses on debt securities, and OTTI losses on debt securities when the entity intends to sell the securities or it is more likely than not that the entity will be required to sell the securities before recovery of its amortized cost basis. Additionally, this item includes OTTI losses recognized during the period on investments accounted for under the cost method of accounting.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 8B -URI http://asc.fasb.org/extlink&oid=27724398&loc=SL6284393-111563
+ Details**Name:**us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionRecognizedInEarningsNet**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                                           |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_AssetBackedSecuritiesMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                                         |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_AssetBackedSecuritiesSecuritizedLoansAndReceivablesMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                 |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_CommonStockMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                             |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_CorporateDebtSecuritiesMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                      |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_EquitySecuritiesMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                           |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_FixedIncomeSecuritiesMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                    |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_PreferredStockMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                         |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_ResidentialMortgageBackedSecuritiesMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                          |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_ShortTermInvestmentsMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                      |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_USStatesAndPoliticalSubdivisionsMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                             |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_USTreasuryAndGovernmentMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |