Unaudited Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Statement of Comprehensive Income [Abstract]
Net income	$ 129.9	$ 207.0
Amortization of prior service credit included in net income	(2.2)	0.0
Postretirement plans and workers’ compensation obligations	(2.2)	0.0
Foreign currency translation adjustment	0.1	(0.8)
Other comprehensive loss, net of income taxes	(2.1)	(0.8)
Comprehensive income	127.8	206.2
Less: Series A Convertible Preferred Stock dividends	0.0	102.5
Less: Net income (loss) attributable to noncontrolling interests	5.7	(2.1)
Comprehensive income attributable to common stockholders	$ 122.1	$ 105.8