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Investments - Net Investment Income and Investment Gains (Losses) (Parenthetical) (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Net Investment Income [Line Items]      
Net unrealized gains (losses) on trading securities $ 41 $ (121) $ 39
Fixed Maturity Securities [Member]      
Net Investment Income [Line Items]      
Gross investment gains on available-for-sale securities 125 168 187
Gross investment losses on available-for-sale securities 131 164 $ 65
Fixed Maturity Securities [Member] | Nonredeemable Preferred Stock [Member]      
Net Investment Income [Line Items]      
Net investment gains (losses) on trading securities $ 66 $ (73)