Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Statement of Comprehensive Income [Abstract]
Net income	$ 21.4	$ (11.0)	$ 54.5	$ (7.6)
Defined benefit pension and other postretirement employee benefits:
Amortization of actuarial loss included in net periodic cost, net of tax of $0.6, $0.4, $1.9, $1.4	1.8	1.3	5.5	3.9
Other comprehensive income (loss), net of tax	1.8	1.3	5.5	3.9
Comprehensive income	23.2	(9.7)	60.0	(3.7)
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, Tax	$ 0.6	$ 0.4	$ 1.9	$ 1.4