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Investments (Net Realized Gains (Losses) From Sales Of Available-For-Sale Securities) (Detail) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2015
Sep. 30, 2014
Sep. 30, 2015
Sep. 30, 2014
Investments [Abstract]        
Proceeds from sales $ 251 $ 131 $ 630 $ 594
Available For Sale Securities Realized Gain Loss [Abstract]        
Gross realized gains 6 4 14 61
Gross realized losses $ (2) $ 0 $ (11) $ (13)