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Investments - Net Investment Income and Investment Gains (Losses) (Parenthetical) (Detail) - USD ($) $ in Millions | 3 Months Ended
--- | ---
Mar. 31, 2019 | Mar. 31, 2018
Net Investment Income [Line Items] |  |
Net unrealized gains (losses) on trading securities | $ 44 | $ (25)
Nonredeemable Preferred Stock [Member] |  |
Net Investment Income [Line Items] |  |
Net realized gains (losses) on trading securities | 42 | (15)
Fixed Maturity Securities [Member] |  |
Net Investment Income [Line Items] |  |
Gross realized gains on available-for-sale securities | 36 | 69
Gross realized losses on available-for-sale securities | $ 42 | $ 51

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- Definition This item represents the gross loss realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. + References No definition available. + Details
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