Accumulated Other Comprehensive Loss (AOCL) - Changes In Components Of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, start	$ 421.0	$ 546.1	$ 675.0
Other comprehensive income (loss) before reclassifications	(5.9)	31.6	(13.5)
Net amount reclassified to net income (loss)	(5.8)	4.9	4.5
Balance, end	399.3	421.0	546.1
Cost of goods sold	2,730.6	2,088.3	1,641.6
Other income, net	15.3	3.1	3.5
Selling, general and administrative expenses	37.5	57.6	43.5
Other operating expense (income), net	0.0	0.6	0.5
Income tax (expense) benefit	47.4	(30.6)	(3.1)
Net loss	14.1	167.1	123.3
Defined benefit plan and other postretirement liabilities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, start	(84.0)	(120.6)	(111.7)
Other comprehensive income (loss) before reclassifications	(5.9)	31.6	(13.5)
Net amount reclassified to net income (loss)	(5.7)	5.0	4.6
Balance, end	(95.6)	(84.0)	(120.6)
Unrealized gain (loss) on financial instruments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, start	1.7	1.8	1.9
Other comprehensive income (loss) before reclassifications	0.0	0.0	0.0
Net amount reclassified to net income (loss)	(0.1)	(0.1)	(0.1)
Balance, end	1.6	1.7	1.8
Accumulated other comprehensive loss
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, start	(82.3)	(118.8)	(109.8)
Balance, end	(94.0)	(82.3)	(118.8)
Reclassification out of Accumulated Other Comprehensive Income | Defined benefit plan and other postretirement liabilities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Cost of goods sold	3.5	26.8	(4.7)
Other income, net	(8.9)	0.0	0.0
Selling, general and administrative expenses	3.3	2.9	(2.0)
Other operating expense (income), net	(9.0)	7.3	(1.1)
Income tax (expense) benefit	(0.3)	(0.4)	(1.1)
Net loss	(11.4)	36.6	(8.9)
Reclassification out of Accumulated Other Comprehensive Income | Unrealized gain (loss) on financial instruments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Cost of goods sold	(0.2)	(0.1)	(0.2)
Income tax (expense) benefit	(0.1)	0.0	0.1
Net loss	$ (0.3)	$ (0.1)	$ (0.1)