Components of Accumulated Other Comprehensive Loss - Reclassifications out of AOCL (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Cost of goods sold	$ (556.7)	$ (680.2)	$ (1,620.6)	$ (2,181.3)
Other income (expense) - net	1.3	11.6	(2.5)	16.7
Selling, general and administrative expenses	(10.8)	(8.7)	(36.2)	(26.2)
Other operating expense (income) - net	(1.9)	0.2	(13.7)	(0.2)
Income tax effect	11.0	(20.6)	21.2	(64.6)
Net (loss) income attributable to Century stockholders	(42.0)	44.3	(73.1)	99.4
Reclassification out of accumulated other comprehensive income | Defined benefit plan and other postretirement liabilities
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Cost of goods sold	1.1	0.4	3.3	1.3
Other income (expense) - net	0.0	(8.0)	0.0	(8.0)
Selling, general and administrative expenses	0.1	0.2	0.4	0.5
Other operating expense (income) - net	0.5	0.2	1.4	0.7
Income tax effect	0.0	(0.1)	0.0	(0.3)
Net (loss) income attributable to Century stockholders	1.7	(7.3)	5.1	(5.8)
Reclassification out of accumulated other comprehensive income | Unrealized gain (loss) on financial instruments
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Cost of goods sold	0.0	0.0	(0.1)	(0.1)
Income tax effect	0.0	0.0	0.0	0.0
Net (loss) income attributable to Century stockholders	$ 0.0	$ 0.0	$ (0.1)	$ (0.1)