Investments (Roll-Forward Of Pre-Tax Credit Losses Related To Fixed Maturities For Which Portion Of Other-Than-Temporary Impairment Was Recognized In Other Comprehensive Income) (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Roll-Forward Of Pre-Tax Credit Losses Related To Fixed Maturities For Which Portion Of Other-Than-Temporary Impairment Was Recognized In Other Comprehensive Income [Roll Forward]
Balance of credit losses related to securities still held – beginning of period	$ 29	$ 51	$ 35	$ 53
Additions where no OTTI was previously recorded	2	4	3	16
Additions where an OTTI was previously recorded	1	1	2	13
Reductions for securities sold during the period	(7)	(11)	(15)	(37)
Balance of credit losses related to securities still held – end of period	$ 25	$ 45	$ 25	$ 45