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Investments - Available for sale fixed maturities (Details) - USD ($) $ in Millions | Jun. 30, 2018 | Dec. 31, 2017
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Schedule of Available-for-sale Securities [Line Items] |  |
Fixed maturities, Available for sale, Amortized Cost | $ 39,244 | $ 37,038
Available for sale (AFS) fixed maturities | 39,648 | 38,379
Total fixed maturities |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Fixed maturities, Available for sale, Amortized Cost | 39,244 | 37,038
Fixed maturities, Available for sale, Gross Unrealized, Gains | 842 | 1,423
Fixed maturities, Available for sale, Gross Unrealized, Losses | (438) | (82)
Fixed maturities, Available for sale, Net Unrealized, Gains (Losses) | 404 | 1,341
Available for sale (AFS) fixed maturities | 39,648 | 38,379
U.S. Government and government agencies |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Fixed maturities, Available for sale, Amortized Cost | 243 | 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 | 240 | 242
States, municipalities and political subdivisions |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Fixed maturities, Available for sale, Amortized Cost | 6,804 | 6,887
Fixed maturities, Available for sale, Gross Unrealized, Gains | 162 | 254
Fixed maturities, Available for sale, Gross Unrealized, Losses | (53) | (18)
Fixed maturities, Available for sale, Net Unrealized, Gains (Losses) | 109 | 236
Available for sale (AFS) fixed maturities | 6,913 | 7,123
Foreign government |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Fixed maturities, Available for sale, Amortized Cost | 127 | 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 | 129 | 127
Residential MBS |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Fixed maturities, Available for sale, Amortized Cost | 2,564 | 2,884
Fixed maturities, Available for sale, Gross Unrealized, Gains | 329 | 349
Fixed maturities, Available for sale, Gross Unrealized, Losses | (7) | (6)
Fixed maturities, Available for sale, Net Unrealized, Gains (Losses) | 322 | 343
Available for sale (AFS) fixed maturities | 2,886 | 3,227
Commercial MBS |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Fixed maturities, Available for sale, Amortized Cost | 920 | 927
Fixed maturities, Available for sale, Gross Unrealized, Gains | 18 | 36
Fixed maturities, Available for sale, Gross Unrealized, Losses | (4) | (1)
Fixed maturities, Available for sale, Net Unrealized, Gains (Losses) | 14 | 35
Available for sale (AFS) fixed maturities | 934 | 962
Asset-backed securities |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Fixed maturities, Available for sale, Amortized Cost | 8,849 | 7,836
Fixed maturities, Available for sale, Gross Unrealized, Gains | 132 | 142
Fixed maturities, Available for sale, Gross Unrealized, Losses | (46) | (16)
Fixed maturities, Available for sale, Net Unrealized, Gains (Losses) | 86 | 126
Available for sale (AFS) fixed maturities | 8,935 | 7,962
Corporate and other |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Fixed maturities, Available for sale, Amortized Cost | 19,737 | 18,136
Fixed maturities, Available for sale, Gross Unrealized, Gains | 198 | 638
Fixed maturities, Available for sale, Gross Unrealized, Losses | (324) | (38)
Fixed maturities, Available for sale, Net Unrealized, Gains (Losses) | (126) | 600
Available for sale (AFS) fixed maturities | $ 19,611 | $ 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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