STATEMENTS OF CONSOLIDATED COMPREHENSIVE (LOSS) INCOME - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Statement Of Income And Comprehensive Income [Abstract]
Net (loss) income	$ (18.5)	$ 28.8	$ 62.0
Other comprehensive (loss) income, net of tax
Defined benefit pension plan and Salaried VEBA	(1.6)	13.4	2.4
Available for sale securities		(0.3)
Cash flow hedges	16.6	6.7	7.8
Foreign currency translation		0.1
Other comprehensive income, net of tax	15.0	19.9	10.2
Comprehensive (loss) income	$ (3.5)	$ 48.7	$ 72.2