Supplemental Balance Sheet Information - Schedule of Supplemental Balance Sheet Information (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Cash and Cash Equivalents
Cash and money market funds	$ 750.1	$ 28.2
Commercial paper		236.1
Total	750.1	264.3
Trade Receivables, Net
Allowance for doubtful receivables	(0.8)	(1.4)
Trade receivables, net	119.0	167.1
Inventories
Finished products	33.2	42.6
Work-in-process	61.9	63.5
Raw materials	55.2	65.0
Operating supplies	7.2	6.5
Total	157.5	177.6
Property, Plant and Equipment, Net
Land and improvements	21.5	21.4
Buildings and leasehold improvements	111.8	104.5
Machinery and equipment	836.3	813.5
Construction in progress	38.2	33.2
Property, plant and equipment, gross	1,007.8	972.6
Accumulated depreciation	(386.6)	(352.2)
Assets held for sale	1.7	1.6
Property, plant and equipment, net	622.9	622.0
Other Accrued Liabilities
Uncleared cash disbursements	2.4	4.2
Accrued income taxes and taxes payable	8.7	6.2
Accrued annual contribution to Salaried VEBA		2.9
Accrued interest	11.7	2.3
Short-term environmental accrual	4.5	5.5
Other	18.0	22.9
Total	45.3	44.0
Long-Term Liabilities
Workers' compensation accrual	30.5	27.7
Long-term environmental accrual	16.2	11.5
Other long-term liabilities	33.6	27.8
Total	80.3	67.0
Billed
Trade Receivables, Net
Billed trade receivables	$ 119.8	$ 168.5