Stockholders' Equity - Schedule Of Stock Repurchase Activities (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Equity [Abstract]
Shares repurchased (shares)	0.1	0.4	2.5
Average price per share (usd per share)	$ 605.10	$ 502.23	$ 397.52
Value of shares repurchased	$ 42.5	$ 183.7	$ 1,000.0