Consolidated Statement of Shareholders' Equity (Unaudited) - 9 months ended Sep. 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	483.7						483.7
Equity-based compensation expense	26.0					26.0
Stock option exercises (in shares)				0.7
Stock option exercises	24.4					24.4
Coworker Stock Purchase Plan (in shares)				0.1
Coworker Stock Purchase Plan	8.4					8.4
Repurchases of common stock (in shares)				(3.0)
Repurchases of common stock	(232.5)						(232.5)
Dividends paid	(95.5)					0.5	(96.0)
Incentive compensation plan shares withheld for taxes (in shares)					(0.1)
Incentive compensation plan stock withheld for taxes	(27.1)						(27.1)
Foreign currency translation	(17.9)	[1]						(17.9)
Unrealized gain from hedge accounting	5.6							5.6
Ending balance (in shares) at Sep. 30, 2018			0.0	150.9	0.0
Ending balance at Sep. 30, 2018	$ 1,160.7		$ 0.0	$ 1.5	$ 0.0	$ 2,970.9	$ (1,703.5)	$ (108.2)

[1] Net of tax expense of $0.1 million and tax expense of $0.3 million for the three months ended September 30, 2018 and 2017, respectively, and net of tax benefit of $0.1 million and tax expense of $0.3 million for the nine months ended September 30, 2018 and 2017, respectively.