Share Repurchase Plan - Schedule of Share Repurchases Under Share Repurchase Plan - (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended			34 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2015
Equity [Abstract]
Total cost of shares repurchased	$ 91	$ 3,722	$ 1,538	$ 5,351
Total number of shares repurchased	1,450	43,350	19,310	64,110
Average cost per share (including transaction fees)	$ 62.76	$ 85.83	$ 79.65	$ 83.45