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Investments - Gross unrealized losses on securities by investment category and length of time that have been in a continuous unrealized loss position (Details) - USD ($) $ in Millions | Mar. 31, 2018 | Dec. 31, 2017
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Total fixed maturities |  |
Available for sale securities in a continuous unrealized loss position |  |
Unrealized Loss - Less than twelve months | $ (203) | $ (37)
Fair Value - Less than twelve months | $ 12,065 | $ 4,295
Fair Value as % of Cost - Less than twelve months | 98.00% | 99.00%
Unrealized Loss - Twelve months or more | $ (60) | $ (45)
Fair Value - Twelve months or more | $ 1,551 | $ 1,574
Fair Value as % of Cost - Twelve months or more | 96.00% | 97.00%
U.S. Government and government agencies |  |
Available for sale securities in a continuous unrealized loss position |  |
Unrealized Loss - Less than twelve months | $ (1) | $ 0
Fair Value - Less than twelve months | $ 57 | $ 55
Fair Value as % of Cost - Less than twelve months | 98.00% | 100.00%
Unrealized Loss - Twelve months or more | $ (3) | $ (3)
Fair Value - Twelve months or more | $ 119 | $ 123
Fair Value as % of Cost - Twelve months or more | 98.00% | 98.00%
States, municipalities and political subdivisions |  |
Available for sale securities in a continuous unrealized loss position |  |
Unrealized Loss - Less than twelve months | $ (26) | $ (8)
Fair Value - Less than twelve months | $ 1,745 | $ 825
Fair Value as % of Cost - Less than twelve months | 99.00% | 99.00%
Unrealized Loss - Twelve months or more | $ (13) | $ (10)
Fair Value - Twelve months or more | $ 411 | $ 431
Fair Value as % of Cost - Twelve months or more | 97.00% | 98.00%
Foreign government |  |
Available for sale securities in a continuous unrealized loss position |  |
Unrealized Loss - Less than twelve months | $ 0 | $ 0
Fair Value - Less than twelve months | $ 22 | $ 4
Fair Value as % of Cost - Less than twelve months | 100.00% | 100.00%
Unrealized Loss - Twelve months or more | $ 0 | $ 0
Fair Value - Twelve months or more | $ 0 | $ 0
Fair Value as % of Cost - Twelve months or more | 0.00% | 0.00%
Residential MBS |  |
Available for sale securities in a continuous unrealized loss position |  |
Unrealized Loss - Less than twelve months | $ (3) | $ (1)
Fair Value - Less than twelve months | $ 155 | $ 118
Fair Value as % of Cost - Less than twelve months | 98.00% | 99.00%
Unrealized Loss - Twelve months or more | $ (4) | $ (5)
Fair Value - Twelve months or more | $ 114 | $ 118
Fair Value as % of Cost - Twelve months or more | 97.00% | 96.00%
Commercial MBS |  |
Available for sale securities in a continuous unrealized loss position |  |
Unrealized Loss - Less than twelve months | $ (3) | $ (1)
Fair Value - Less than twelve months | $ 148 | $ 67
Fair Value as % of Cost - Less than twelve months | 98.00% | 99.00%
Unrealized Loss - Twelve months or more | $ 0 | $ 0
Fair Value - Twelve months or more | $ 0 | $ 0
Fair Value as % of Cost - Twelve months or more | 0.00% | 0.00%
Asset-backed securities |  |
Available for sale securities in a continuous unrealized loss position |  |
Unrealized Loss - Less than twelve months | $ (21) | $ (7)
Fair Value - Less than twelve months | $ 2,586 | $ 1,195
Fair Value as % of Cost - Less than twelve months | 99.00% | 99.00%
Unrealized Loss - Twelve months or more | $ (10) | $ (9)
Fair Value - Twelve months or more | $ 306 | $ 299
Fair Value as % of Cost - Twelve months or more | 97.00% | 97.00%
Corporate and other |  |
Available for sale securities in a continuous unrealized loss position |  |
Unrealized Loss - Less than twelve months | $ (149) | $ (20)
Fair Value - Less than twelve months | $ 7,352 | $ 2,031
Fair Value as % of Cost - Less than twelve months | 98.00% | 99.00%
Unrealized Loss - Twelve months or more | $ (30) | $ (18)
Fair Value - Twelve months or more | $ 601 | $ 603
Fair Value as % of Cost - Twelve months or more | 95.00% | 97.00%
Total equity securities |  |
Available for sale securities in a continuous unrealized loss position |  |
Unrealized Loss - Less than twelve months |  | $ (22)
Fair Value - Less than twelve months |  | $ 158
Fair Value as % of Cost - Less than twelve months |  | 88.00%
Unrealized Loss - Twelve months or more |  | $ (1)
Fair Value - Twelve months or more |  | $ 13
Fair Value as % of Cost - Twelve months or more |  | 93.00%
Common stocks |  |
Available for sale securities in a continuous unrealized loss position |  |
Unrealized Loss - Less than twelve months |  | $ (22)
Fair Value - Less than twelve months |  | $ 117
Fair Value as % of Cost - Less than twelve months |  | 84.00%
Unrealized Loss - Twelve months or more |  | $ 0
Fair Value - Twelve months or more |  | $ 0
Fair Value as % of Cost - Twelve months or more |  | 0.00%
Perpetual preferred stocks |  |
Available for sale securities in a continuous unrealized loss position |  |
Unrealized Loss - Less than twelve months |  | $ 0
Fair Value - Less than twelve months |  | $ 41
Fair Value as % of Cost - Less than twelve months |  | 100.00%
Unrealized Loss - Twelve months or more |  | $ (1)
Fair Value - Twelve months or more |  | $ 13
Fair Value as % of Cost - Twelve months or more |  | 93.00%

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