Consolidated Statement of Shareholders' Equity (Unaudited) - 6 months ended Jun. 30, 2018 - USD ($) shares in Millions, $ in Millions	Total		Preferred Stock	Common Stock	Treasury Stock	Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive Loss
Beginning balance (in shares) at Dec. 31, 2017			0.0	153.1	0.1
Beginning balance at Dec. 31, 2017	$ 982.9		$ 0.0	$ 1.5	$ 0.0	$ 2,911.6	$ (1,834.3)	$ (95.9)
Cumulative adjustment upon adoption of ASC 606 at Dec. 31, 2017	2.7						2.7
Balance as of December 31, 2017 (as adjusted) at Dec. 31, 2017	985.6		$ 0.0	$ 1.5	$ 0.0	2,911.6	(1,831.6)	(95.9)
Shareholders' Equity (Deficit) [Roll Forward]
Net income	300.0						300.0
Equity-based compensation expense	16.1					16.1
Stock option exercises (in shares)				0.7
Stock option exercises	19.9					19.9
Coworker Stock Purchase Plan (in shares)				0.1
Coworker Stock Purchase Plan	5.4					5.4
Repurchases of common stock (in shares)				(2.4)
Repurchases of common stock	(176.4)						(176.4)
Dividends paid	(63.8)					0.3	(64.1)
Incentive compensation plan shares withheld for taxes (in shares)					(0.1)
Incentive compensation plan stock withheld for taxes	(8.7)						(8.7)
Foreign currency translation	(14.7)	[1]						(14.7)
Unrealized gain from hedge accounting	5.5							5.5
Ending balance (in shares) at Jun. 30, 2018			0.0	151.5	0.0
Ending balance at Jun. 30, 2018	$ 1,068.9		$ 0.0	$ 1.5	$ 0.0	$ 2,953.3	$ (1,780.8)	$ (105.1)

[1] (1)Net of tax benefit of $0.1 million for both the three months ended June 30, 2018 and 2017, and net of tax benefit of $0.2 million and $0.1 million for the six months ended June 30, 2018 and 2017, respectively.