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Investments - Available for sale fixed maturities (Details) - USD ($) $ in Millions | Mar. 31, 2018 | Dec. 31, 2017
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Schedule of Available-for-sale Securities [Line Items] |  |
Fixed maturities, Available for sale, Amortized Cost | $ 38,383 | $ 37,038
Available for sale (AFS) fixed maturities | 39,125 | 38,379
Total fixed maturities |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Fixed maturities, Available for sale, Amortized Cost | 38,383 | 37,038
Fixed maturities, Available for sale, Gross Unrealized, Gains | 1,005 | 1,423
Fixed maturities, Available for sale, Gross Unrealized, Losses | (263) | (82)
Fixed maturities, Available for sale, Net Unrealized, Gains (Losses) | 742 | 1,341
Available for sale (AFS) fixed maturities | 39,125 | 38,379
U.S. Government and government agencies |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Fixed maturities, Available for sale, Amortized Cost | 253 | 244
Fixed maturities, Available for sale, Gross Unrealized, Gains | 1 | 1
Fixed maturities, Available for sale, Gross Unrealized, Losses | (4) | (3)
Fixed maturities, Available for sale, Net Unrealized, Gains (Losses) | (3) | (2)
Available for sale (AFS) fixed maturities | 250 | 242
States, municipalities and political subdivisions |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Fixed maturities, Available for sale, Amortized Cost | 6,855 | 6,887
Fixed maturities, Available for sale, Gross Unrealized, Gains | 187 | 254
Fixed maturities, Available for sale, Gross Unrealized, Losses | (39) | (18)
Fixed maturities, Available for sale, Net Unrealized, Gains (Losses) | 148 | 236
Available for sale (AFS) fixed maturities | 7,003 | 7,123
Foreign government |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Fixed maturities, Available for sale, Amortized Cost | 130 | 124
Fixed maturities, Available for sale, Gross Unrealized, Gains | 2 | 3
Fixed maturities, Available for sale, Gross Unrealized, Losses | 0 | 0
Fixed maturities, Available for sale, Net Unrealized, Gains (Losses) | 2 | 3
Available for sale (AFS) fixed maturities | 132 | 127
Residential MBS |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Fixed maturities, Available for sale, Amortized Cost | 2,732 | 2,884
Fixed maturities, Available for sale, Gross Unrealized, Gains | 338 | 349
Fixed maturities, Available for sale, Gross Unrealized, Losses | (7) | (6)
Fixed maturities, Available for sale, Net Unrealized, Gains (Losses) | 331 | 343
Available for sale (AFS) fixed maturities | 3,063 | 3,227
Commercial MBS |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Fixed maturities, Available for sale, Amortized Cost | 922 | 927
Fixed maturities, Available for sale, Gross Unrealized, Gains | 21 | 36
Fixed maturities, Available for sale, Gross Unrealized, Losses | (3) | (1)
Fixed maturities, Available for sale, Net Unrealized, Gains (Losses) | 18 | 35
Available for sale (AFS) fixed maturities | 940 | 962
Asset-backed securities |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Fixed maturities, Available for sale, Amortized Cost | 8,546 | 7,836
Fixed maturities, Available for sale, Gross Unrealized, Gains | 148 | 142
Fixed maturities, Available for sale, Gross Unrealized, Losses | (31) | (16)
Fixed maturities, Available for sale, Net Unrealized, Gains (Losses) | 117 | 126
Available for sale (AFS) fixed maturities | 8,663 | 7,962
Corporate and other |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Fixed maturities, Available for sale, Amortized Cost | 18,945 | 18,136
Fixed maturities, Available for sale, Gross Unrealized, Gains | 308 | 638
Fixed maturities, Available for sale, Gross Unrealized, Losses | (179) | (38)
Fixed maturities, Available for sale, Net Unrealized, Gains (Losses) | 129 | 600
Available for sale (AFS) fixed maturities | $ 19,074 | $ 18,736

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- Definition Amount before tax of net unrealized gain (loss) in accumulated other comprehensive income (AOCI) on investments in debt securities classified as available-for-sale. + References No definition available. + Details
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