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Stockholders' Equity - Schedule Of Stock Repurchase Activities (Detail) - USD ($)
$ / shares in Units, shares in Millions, $ in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Equity [Abstract]      
Shares repurchased (shares) 7.3 0.2 1.1
Average price per share (usd per share) $ 310.32 $ 201.70 $ 167.41
Value of shares repurchased $ 2,274.0 $ 42.5 $ 183.7