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Investments - Narrative (Details) $ in Millions | 12 Months Ended
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Dec. 31, 2017 USD ($) security | Dec. 31, 2016 USD ($) | Dec. 31, 2015 USD ($)
Investment [Line Items] |  |  |
Percentage (based on amount of unrealized loss) of available for sale fixed maturities that are in an unrealized loss position and rated investment grade | 78.00% |  |
Percentage (based on fair value) of available for sale fixed maturities that are in an unrealized loss position and rated investment grade | 90.00% |  |
Other than temporary impairment charges | $ 73 | $ 116 | $ 125
Average life of ABS | 5 years |  |
Average life of MBS | 4 years 6 months |  |
Residential MBS |  |  |
Investment [Line Items] |  |  |
Non-credit related portion of other-than-temporary impairment charges taken for securities still owned | $ 158 | 189 |
Fixed maturities, Gross Unrealized, Losses | (6) | (13) |
Other than temporary impairment charges | 1 |  |
Fixed Maturities excluding Residential MBS |  |  |
Investment [Line Items] |  |  |
Other than temporary impairment charges | 19 |  |
Securities with non-credit other-than-temporary impairment charges |  |  |
Investment [Line Items] |  |  |
Gross Unrealized, Gains | 137 | 130 |
Gross Unrealized, Losses | (4) | (3) |
Fixed maturities |  |  |
Investment [Line Items] |  |  |
Fixed maturities, Gross Unrealized, Losses | $ (82) | (245) |
Number of available for sale securities in an unrealized loss position | security | 841 |  |
Other than temporary impairment charges | $ 20 | 38 | $ 43
Other investments |  |  |
Investment [Line Items] |  |  |
Other than temporary impairment charges | $ 4 |  |
Common stocks |  |  |
Investment [Line Items] |  |  |
Number of available for sale securities in an unrealized loss position | security | 16 |  |
Other than temporary impairment charges | $ 55 |  |
Equity securities, Gross Unrealized, Losses | $ (22) | (23) |
Preferred stocks |  |  |
Investment [Line Items] |  |  |
Number of available for sale securities in an unrealized loss position | security | 7 |  |
Other than temporary impairment charges | $ 9 |  |
Equity securities, Gross Unrealized, Losses | $ (1) | $ (7) |
Number of available for sale securities in an unrealized loss position for twelve months or longer | Common stocks |  |  |
Investment [Line Items] |  |  |
Number of available for sale securities in an unrealized loss position | security | 0 |  |
Number of available for sale securities in an unrealized loss position for twelve months or longer | Preferred stocks |  |  |
Investment [Line Items] |  |  |
Number of available for sale securities in an unrealized loss position | security | 3 |  |

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