CONSOLIDATED STATEMENTS OF STOCKHOLDERS' DEFICIT - USD ($) $ in Millions	Total	Common stock:	Additional paid-in capital:	Accumulated loss:	Treasury stock:	Accumulated other comprehensive loss:
Beginning balance at Dec. 31, 2015		$ 1.0	$ 765.9	$ (1,865.0)		$ (222.2)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuances and purchases of common stock		0.0
Issuance of common stock in connection with employee stock purchase plan			0.0
Net redemption of common stock in connection with stock options and RSUs			(6.1)
Stock-based compensation			33.7
Tax effect from employee stock options and RSUs			(2.7)
Net loss	$ (353.7)			(353.7)
Other comprehensive (loss) income	(111.4)					(111.4)
Ending balance at Dec. 31, 2016	(1,935.7)	1.0	790.8	(2,218.7)	$ (175.2)	(333.6)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuances and purchases of common stock		0.1
Issuance of common stock in connection with employee stock purchase plan			0.8
Net redemption of common stock in connection with stock options and RSUs			(7.1)
Stock-based compensation			23.3
Tax effect from employee stock options and RSUs			0.0
Net loss	(242.3)			(242.3)
Other comprehensive (loss) income	133.9					133.9
Ending balance at Dec. 31, 2017	(2,027.0)	1.1	807.8	(2,461.0)	(175.2)	(199.7)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuances and purchases of common stock		0.0
Issuance of common stock in connection with employee stock purchase plan			0.0
Net redemption of common stock in connection with stock options and RSUs			(15.5)
Stock-based compensation			42.4
Tax effect from employee stock options and RSUs			0.0
Net loss	(352.4)			(352.4)
Other comprehensive (loss) income	(99.8)					(99.8)
Ending balance at Dec. 31, 2018	$ (2,463.2)	$ 1.1	$ 834.7	$ (2,824.3)	$ (175.2)	$ (299.5)