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Investments - Narrative (Details) - USD ($) | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2019 | Sep. 30, 2018 | Sep. 30, 2019 | Sep. 30, 2018 | Dec. 31, 2018
Investment [Line Items] |  |  |  |  |
Gross gains on fixed income securities | $ 168,000,000 | $ 21,000,000 | $ 409,000,000 | $ 95,000,000 |
Gross loss on fixed income securities | (20,000,000) | (48,000,000) | (107,000,000) | (242,000,000) |
Net unrealized gains related to changes in valuation of fixed income securities subsequent to impairment measurement date | 179,000,000 |  | 179,000,000 |  | $ 180,000,000
Limited partnership interests | 7,990,000,000 |  | 7,990,000,000 |  | 7,505,000,000
Short-term investments | 5,254,000,000 |  | 5,254,000,000 |  | 3,027,000,000
EMA limited partnerships |  |  |  |  |
Investment [Line Items] |  |  |  |  |
Limited partnership interests | 6,230,000,000 |  | 6,230,000,000 |  | 5,730,000,000
Limited partnership interests |  |  |  |  |
Investment [Line Items] |  |  |  |  |
Limited partnership interests | 1,760,000,000 |  | 1,760,000,000 |  | $ 1,780,000,000
Mortgage loans, non-impaired |  |  |  |  |
Investment [Line Items] |  |  |  |  |
Allowance for credit losses, period increase (decrease) | 0 | 0 | 0 | 0 |
Average impaired mortgage loans | $ 4,000,000 | $ 4,000,000 | $ 4,000,000 | $ 4,000,000 |

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