v3.8.0.1
Investments (Fair Value and Losses by Investment Category and Length of Time in a Loss Position) (Details) - USD ($)
$ in Millions
Dec. 31, 2017
Dec. 31, 2016
Fixed maturities    
Schedule of Available-for-sale Securities [Line Items]    
Less than twelve months, Fair Value $ 27,635 $ 68,613
Less than twelve months, Gross Unrealized Loss 333 3,205
Twelve months or more, Fair Value 28,336 12,250
Twelve months or more, Gross Unrealized Losses 1,443 1,420
Total, Fair Value 55,971 80,863
Total, Gross Unrealized Losses 1,776 4,625
Fair Value not reflected in AOCI, held-to-maturity securities 12 12
Gross Unrealized Losses not reflected in AOCI, held-to-maturity securities 1 1
Fixed maturities | U.S. Treasury securities and obligations of U.S. government authorities and agencies    
Schedule of Available-for-sale Securities [Line Items]    
Less than twelve months, Fair Value 3,450 9,345
Less than twelve months, Gross Unrealized Loss 28 1,001
Twelve months or more, Fair Value 6,391 0
Twelve months or more, Gross Unrealized Losses 318 0
Total, Fair Value 9,841 9,345
Total, Gross Unrealized Losses 346 1,001
Fixed maturities | Obligations of U.S. states and their political subdivisions    
Schedule of Available-for-sale Securities [Line Items]    
Less than twelve months, Fair Value 44 2,677
Less than twelve months, Gross Unrealized Loss 0 79
Twelve months or more, Fair Value 287 19
Twelve months or more, Gross Unrealized Losses 6 5
Total, Fair Value 331 2,696
Total, Gross Unrealized Losses 6 84
Fixed maturities | Foreign government bonds    
Schedule of Available-for-sale Securities [Line Items]    
Less than twelve months, Fair Value 4,417 6,076
Less than twelve months, Gross Unrealized Loss 55 325
Twelve months or more, Fair Value 2,937 310
Twelve months or more, Gross Unrealized Losses 238 29
Total, Fair Value 7,354 6,386
Total, Gross Unrealized Losses 293 354
Fixed maturities | U.S. corporate public securities    
Schedule of Available-for-sale Securities [Line Items]    
Less than twelve months, Fair Value 7,914 22,803
Less than twelve months, Gross Unrealized Loss 110 905
Twelve months or more, Fair Value 6,831 2,943
Twelve months or more, Gross Unrealized Losses 304 327
Total, Fair Value 14,745 25,746
Total, Gross Unrealized Losses 414 1,232
Fixed maturities | U.S. corporate private securities    
Schedule of Available-for-sale Securities [Line Items]    
Less than twelve months, Fair Value 4,596 7,797
Less than twelve months, Gross Unrealized Loss 76 228
Twelve months or more, Fair Value 2,009 1,296
Twelve months or more, Gross Unrealized Losses 93 80
Total, Fair Value 6,605 9,093
Total, Gross Unrealized Losses 169 308
Fixed maturities | Foreign corporate public securities    
Schedule of Available-for-sale Securities [Line Items]    
Less than twelve months, Fair Value 2,260 5,196
Less than twelve months, Gross Unrealized Loss 21 162
Twelve months or more, Fair Value 1,678 1,047
Twelve months or more, Gross Unrealized Losses 78 143
Total, Fair Value 3,938 6,243
Total, Gross Unrealized Losses 99 305
Fixed maturities | Foreign corporate private securities    
Schedule of Available-for-sale Securities [Line Items]    
Less than twelve months, Fair Value 1,213 6,557
Less than twelve months, Gross Unrealized Loss 20 350
Twelve months or more, Fair Value 5,339 4,916
Twelve months or more, Gross Unrealized Losses 317 799
Total, Fair Value 6,552 11,473
Total, Gross Unrealized Losses 337 1,149
Fixed maturities | Commercial mortgage-backed securities    
Schedule of Available-for-sale Securities [Line Items]    
Less than twelve months, Fair Value 2,593 4,879
Less than twelve months, Gross Unrealized Loss 17 123
Twelve months or more, Fair Value 2,212 60
Twelve months or more, Gross Unrealized Losses 74 2
Total, Fair Value 4,805 4,939
Total, Gross Unrealized Losses 91 125
Fixed maturities | Asset-backed securities    
Schedule of Available-for-sale Securities [Line Items]    
Less than twelve months, Fair Value 564 2,357
Less than twelve months, Gross Unrealized Loss 2 20
Twelve months or more, Fair Value 366 1,581
Twelve months or more, Gross Unrealized Losses 8 33
Total, Fair Value 930 3,938
Total, Gross Unrealized Losses 10 53
Fixed maturities | Residential mortgage-backed securities    
Schedule of Available-for-sale Securities [Line Items]    
Less than twelve months, Fair Value 584 926
Less than twelve months, Gross Unrealized Loss 4 12
Twelve months or more, Fair Value 286 78
Twelve months or more, Gross Unrealized Losses 7 2
Total, Fair Value 870 1,004
Total, Gross Unrealized Losses 11 14
Equity securities    
Schedule of Available-for-sale Securities [Line Items]    
Less than twelve months, Fair Value 358 637
Less than twelve months, Gross Unrealized Loss 28 41
Twelve months or more, Fair Value 0 12
Twelve months or more, Gross Unrealized Losses 1 1
Total, Fair Value 358 649
Total, Gross Unrealized Losses $ 29 $ 42