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Investments (Net Realized Gains (Losses) From Sales Of Available-For-Sale Securities) (Detail) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2020
Jun. 30, 2019
Jun. 30, 2020
Jun. 30, 2019
Investments [Abstract]        
Proceeds from sales $ 290 $ 684 $ 569 $ 1,367
Available For Sale Securities Realized Gain Loss [Abstract]        
Gross realized gains 20 16 31 21
Gross realized losses $ (4) $ (2) $ (12) $ (3)