Common Stock Repurchase Program (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	1 Months Ended	3 Months Ended
	Jan. 31, 2019	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017
Accelerated Share Repurchases [Line Items]
Total repurchases		$ 64.0	$ 258.0
Authorized share repurchases				$ 1,500.0	$ 1,250.0
Cash paid for repurchase of common stock		$ 68.0	$ 250.0
10b5-1 Plan [Member]
Accelerated Share Repurchases [Line Items]
Shares repurchased		0.7
Total repurchases		$ 64.0
Weighted average per share purchase price		$ 94.35
Cash paid for repurchase of common stock	$ 4.0