Unaudited Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Statement of Comprehensive Income [Abstract]
Net income	$ 39.5	$ 116.4	$ 169.4	$ 323.4
Postretirement plans and workers’ compensation obligations (net of $0.0 tax provisions in each period)	(2.2)	0.0	(4.4)	0.0
Foreign currency translation adjustment	(0.5)	(2.2)	(0.4)	(3.0)
Other comprehensive loss, net of income taxes	(2.7)	(2.2)	(4.8)	(3.0)
Comprehensive income	36.8	114.2	164.6	320.4
Less: Series A Convertible Preferred Stock dividends	0.0	0.0	0.0	102.5
Less: Net income attributable to noncontrolling interests	2.4	2.7	8.1	0.6
Comprehensive income attributable to common stockholders	$ 34.4	$ 111.5	$ 156.5	$ 217.3