Earnings per Share - Computation of Basic and Diluted EPS (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Earnings Per Share [Abstract]
Net income	$ 99.2	$ 80.8
Shares:
Weighted average common shares outstanding — used in calculation of basic EPS	255.3	251.5
Weighted average common stock equivalents — stock options and restricted shares	10.3	12.2
Weighted average common and common equivalent shares outstanding — used in calculation of diluted EPS	265.6	263.7
Earnings per share - Basic	$ 0.39	$ 0.32
Earnings per share - Diluted	$ 0.37	$ 0.31