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, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 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	$ 15	$ 32	$ 22	$ 35
Additions where no OTTI was previously recorded	1	1	1	1
Additions where an OTTI was previously recorded	0	0	0	1
Reductions for securities sold during the period	0	(4)	(7)	(8)
Balance of credit losses related to securities still held – end of period	$ 16	$ 29	$ 16	$ 29