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		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 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	$ 32	$ 57	$ 35	$ 53
Additions where no OTTI was previously recorded	1	1	1	12
Additions where an OTTI was previously recorded	0	6	1	12
Reductions for securities sold during the period	(4)	(13)	(8)	(26)
Balance of credit losses related to securities still held – end of period	$ 29	$ 51	$ 29	$ 51