Components of Accumulated Other Comprehensive Loss - Components of AOCI (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive loss before income tax effect	$ (84.1)		$ (84.8)
Income tax effect	2.4		2.5
Accumulated other comprehensive loss	(81.7)		(82.3)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, start	421.0	$ 546.1
Net amount reclassified to net income (loss)	0.6	1.3
Balance, end	439.8	408.3
Defined benefit plan and other postretirement liabilities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive loss before income tax effect	(86.0)		(86.7)
Income tax effect	2.8		2.9
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, start	(84.0)	(120.6)
Net amount reclassified to net income (loss)	0.6	1.3
Balance, end	(83.4)	(119.3)
Unrealized gain (loss) on financial instruments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive loss before income tax effect	1.9		1.9
Income tax effect	(0.4)		$ (0.4)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, start	1.7	1.8
Net amount reclassified to net income (loss)	0.0	(0.0)
Balance, end	1.7	1.8
Accumulated other comprehensive loss [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, start	(82.3)	(118.8)
Balance, end	$ (81.7)	$ (117.5)