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Investments - OTTI OCI (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]      
Document Period End Date Dec. 31, 2019    
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]      
Balance, beginning $ 5 $ 16 $ 9
Additional Credit Impairments [Abstract]      
On securities not previously impaired 0 0 9
On securities previously impaired 0 1 0
Reductions [Abstract]      
Securities intent impaired 0 12 0
Increase in cash flows 0 0 0
Securities sold, matured, prepaid, or paid down 1 0 2
Balance, ending $ 4 $ 5 $ 16