Share Repurchase Plan - Schedule of Share Repurchases Under Share Repurchase Plan - (Detail) - USD ($) shares in Thousands, $ in Millions	12 Months Ended			46 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2016
Equity [Abstract]
Total cost of shares repurchased	$ 0	$ 91	$ 3,722	$ 5,351
Total number of shares repurchased	0	1,450	43,350	64,110