Investments (Net Realized Gains (Losses) From Sales Of Available-For-Sale Securities) (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Investments [Abstract]
Proceeds from sales	$ 848	$ 251	$ 1,785	$ 630
Available For Sale Securities Realized Gain Loss [Abstract]
Gross realized gains	33	6	70	14
Gross realized losses	$ 0	$ (2)	$ (18)	$ (11)