Investments - Schedule of Net Change in Unrealized Gains (Losses) on Available-for-Sale Investments (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Total net change in unrealized gains (losses) on available-for-sale investments	$ 224	$ (1,119)	$ 1,517
Fixed Maturity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total net change in unrealized gains (losses) on available-for-sale investments	225	(1,114)	1,511
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total net change in unrealized gains (losses) on available-for-sale investments	(2)	(6)	$ 6
Other [Member]
Schedule of Available-for-sale Securities [Line Items]
Total net change in unrealized gains (losses) on available-for-sale investments	$ 1	$ 1