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	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Roll-Forward Of Pre-Tax Credit Losses Related To Fixed Maturities For Which Portion Of OTTI Was Recognized In OCI
Balance of credit losses related to securities still held-beginning of period	$ 35	$ 53	$ 28
Additions where no OTTI was previously recorded	4	17	41
Additions where an OTTI was previously recorded	2	14	9
Reductions for securities sold during the period	(19)	(49)	(25)
Balance of credit losses related to securities still held-end of period	$ 22	$ 35	$ 53