Investments (Net Realized Gains (Losses) From Sales Of Available-For-Sale Securities) (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Investments [Abstract]
Proceeds from sales	$ 656	$ 187	$ 937	$ 379
Available For Sale Securities Realized Gain Loss [Abstract]
Gross realized gains	26	3	37	8
Gross realized losses	$ (13)	$ (2)	$ (18)	$ (9)