Other Assets (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2021	Dec. 31, 2020	Oct. 01, 2020	Dec. 31, 2019
Other Assets [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	$ 234.0	$ 222.9
Finite-Lived Intangible Asset, Expected Amortization, Remainder of Fiscal Year	3.8
Finite-Lived Intangible Asset, Expected Amortization, Year One	14.3
Finite-Lived Intangible Asset, Expected Amortization, Year Two	14.3
Finite-Lived Intangible Asset, Expected Amortization, Year Three	14.3
Finite-Lived Intangible Asset, Expected Amortization, Year Four	14.3
Finite-Lived Intangible Asset, Expected Amortization, Year Five	$ 14.3
Finite-Lived Intangible Assets, Remaining Amortization Period	15 years 6 months
Intangible assets
Deferred financing costs, net	$ 0.3	0.4
Goodwill	623.6	565.3
Equity in net assets of affiliates	1.7	3.1
Customer Supply Agreement	9.7	11.4
Restricted Cash, Noncurrent	19.5	19.5	$ 19.5	$ 16.4
Other	72.2	49.2
Total other long-term assets	103.4	83.6
Prepaid Expense, Current	28.0	16.3
Income Taxes Receivable, Current	88.0	315.3
Other Assets, Miscellaneous, Current	5.1	4.7
Intangible Assets, Net (Excluding Goodwill)	216.2	215.2
Other Assets, Current	121.1	336.3
Patents [Member]
Other Assets [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	2.0	2.0
Finite-Lived Intangible Asset, Expected Amortization, Remainder of Fiscal Year	2.3
Finite-Lived Intangible Asset, Expected Amortization, Year One	8.1
Finite-Lived Intangible Asset, Expected Amortization, Year Two	8.1
Finite-Lived Intangible Asset, Expected Amortization, Year Three	8.1
Finite-Lived Intangible Asset, Expected Amortization, Year Four	8.1
Finite-Lived Intangible Asset, Expected Amortization, Year Five	$ 8.1
Finite-Lived Intangible Assets, Remaining Amortization Period	16 years 8 months 12 days
Intangible assets
Less: Accumulated amortization	$ (2.0)	(2.0)
Favorable Leasehold [Member]
Other Assets [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	2.8	2.8
Finite-Lived Intangible Asset, Expected Amortization, Remainder of Fiscal Year	0.0
Finite-Lived Intangible Asset, Expected Amortization, Year One	0.1
Finite-Lived Intangible Asset, Expected Amortization, Year Two	0.1
Finite-Lived Intangible Asset, Expected Amortization, Year Three	0.1
Finite-Lived Intangible Asset, Expected Amortization, Year Four	0.1
Finite-Lived Intangible Asset, Expected Amortization, Year Five	$ 0.1
Finite-Lived Intangible Assets, Remaining Amortization Period	7 years 10 months 24 days
Intangible assets
Less: Accumulated amortization	$ (1.9)	(1.8)
Debt issuance costs [Member]
Intangible assets
Deferred financing costs	0.9	0.9
Less: Accumulated amortization-deferred financing costs	(0.6)	(0.5)
Developed Technology [Member]
Other Assets [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	92.0	94.0
Finite-Lived Intangible Asset, Expected Amortization, Remainder of Fiscal Year	1.5
Finite-Lived Intangible Asset, Expected Amortization, Year One	6.1
Finite-Lived Intangible Asset, Expected Amortization, Year Two	6.1
Finite-Lived Intangible Asset, Expected Amortization, Year Three	6.1
Finite-Lived Intangible Asset, Expected Amortization, Year Four	6.1
Finite-Lived Intangible Asset, Expected Amortization, Year Five	$ 6.1
Finite-Lived Intangible Assets, Remaining Amortization Period	13 years 9 months 18 days
Intangible assets
Less: Accumulated amortization	$ (7.3)	(2.6)
Customer Relationships
Other Assets [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	137.2	124.1
Intangible assets
Less: Accumulated amortization	$ (6.6)	$ (1.3)