Investments - Appreciation (Depreciation) on Fixed Maturities (Details) (USD $)
In Millions, unless otherwise specified
Mar. 31, 2015
Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost $ 17,252 $ 17,278
Unrealized Appreciation 1,936 1,747
Unrealized (Depreciation) (47) (42)
Total Fair Value 19,141 18,983
Run-off Settlement Annuity Business [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Unrealized Appreciation 820 758
Unrealized (Depreciation) (3) (2)
Total Fair Value 3,200 3,100
Federal government and agency [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 568 608
Unrealized Appreciation 355 346
Unrealized (Depreciation) 0 0
Total Fair Value 923 954
State and local government [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 1,662 1,682
Unrealized Appreciation 172 176
Unrealized (Depreciation) (2) (2)
Total Fair Value 1,832 1,856
Foreign government [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 1,807 1,824
Unrealized Appreciation 153 121
Unrealized (Depreciation) (4) (5)
Total Fair Value 1,956 1,940
Corporate [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 12,600 12,517
Unrealized Appreciation 1,159 1,014
Unrealized (Depreciation) (38) (33)
Total Fair Value 13,721 13,498
Mortgage-backed [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 62 83
Unrealized Appreciation 3 3
Unrealized (Depreciation) (1) (1)
Total Fair Value 64 85
Other asset-backed [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 553 564
Unrealized Appreciation 94 87
Unrealized (Depreciation) (2) (1)
Total Fair Value $ 645 $ 650