Unaudited Condensed Consolidated Statement Of Shareholders' Equity - 6 months ended Jun. 30, 2017 - USD ($) $ in Millions	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Retained Earnings [Member]	Treasury Stock [Member]
BALANCE at period start (in shares) at Dec. 31, 2016		120,562,149
BALANCE at period start at Dec. 31, 2016	$ 2,310.3	$ 1.2	$ 18.2	$ 3,133.3	$ (842.4)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	185.8			185.8
Repurchases of common stock	(35.9)				(35.9)
Stock-based compensation expense	15.5		15.5
Shares awarded under stock-based compensation plans	22.8		(6.1)		28.9
Other	0.1		0.2	(0.1)
BALANCE at period end (in shares) at Jun. 30, 2017		120,562,149
BALANCE at period end at Jun. 30, 2017	$ 2,498.6	$ 1.2	$ 27.8	$ 3,319.0	$ (849.4)