UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS’ EQUITY - USD ($) $ in Millions	Total	Common Stock	Additional paid-in capital	Treasury stock	(Accumulated deficit) retained earnings	Accumulated other comprehensive income	Noncontrolling interests
Balance, beginning of period at Dec. 31, 2019		$ 1.4	$ 3,351.1	$ (1,367.3)	$ 597.0	$ 31.6	$ 58.7
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based compensation for equity-classified awards			2.2
Net loss	$ (131.5)				(129.7)		(1.8)
Repurchase of employee common stock relinquished for tax withholding	0.8			(0.8)
Postretirement plans (net of $0.0 tax provisions in each period)	(2.2)					(2.2)
Foreign currency translation adjustment	(6.8)					(6.8)
Distributions to noncontrolling interests							(0.1)
Balance, end of period at Mar. 31, 2020	2,533.3	1.4	3,353.3	(1,368.1)	467.3	22.6	56.8
Balance, beginning of period at Dec. 31, 2020	981.3	1.4	3,364.6	(1,368.9)	(1,273.3)	205.8	51.7
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based compensation for equity-classified awards			1.8
Net loss	(79.7)				(80.1)		0.4
Repurchase of employee common stock relinquished for tax withholding	0.6			(0.6)
Postretirement plans (net of $0.0 tax provisions in each period)	(11.0)					(11.0)
Foreign currency translation adjustment	(0.2)					(0.2)
Distributions to noncontrolling interests							(0.1)
Balance, end of period at Mar. 31, 2021	$ 891.5	$ 1.4	$ 3,366.4	$ (1,369.5)	$ (1,353.4)	$ 194.6	$ 52.0