Capital Stock and Earnings per Share - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share [Abstract]
Preferred stock, shares authorized	250,000,000
Preferred stock, shares issued	0
Preferred stock, shares outstanding	0
Options to purchase shares of common stock not included in the computation of diluted earnings per share	1,000,000	900,000	500,000
Repurchased shares of common stock		4,200,000
Average price per share		$ 98.50
Total cash outlay		$ 415.5	$ 150.0