Consolidated Statement of Stockholders' Equity - USD ($) $ in Millions	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income	Treasury Stock
Beginning balance at Dec. 31, 2015					$ 118.5
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 220.4
Other comprehensive income	106.6
Ending balance at Mar. 31, 2016					225.1
Beginning balance at Dec. 31, 2016	4,098.1	$ 1.5	$ 3,175.9	$ 5,296.7	94.6	$ (4,470.6)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock plan exercises	(4.2)		(4.2)
Stock plan compensation	1.8		1.8
Dividends	(29.7)			(29.7)
Acquisition of common stock	(104.7)					(104.7)
Net income	143.8			143.8
Other comprehensive income	53.7				53.7
Ending balance at Mar. 31, 2017	$ 4,158.8	$ 1.5	$ 3,173.5	$ 5,410.8	$ 148.3	$ (4,575.3)