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
	Mar. 31, 2018	Mar. 31, 2017
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	$ 22	$ 35
Additions where no OTTI was previously recorded	0	0
Additions where an OTTI was previously recorded	0	1
Reductions for securities sold during the period	(7)	(4)
Balance of credit losses related to securities still held – end of period	$ 15	$ 32