Benefit Expenses Excluded From Activity in Benefits Payable (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Abstract]
Premium deficiency reserve for short-duration policies	$ 176	$ 176	$ 0	$ 0
Military services		12	11	(27)
Future policy benefits		(80)	32	354
Total		$ 108	$ 43	$ 327