Supplemental Balance Sheet Information (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Cash and Cash Equivalents
Cash and money market funds	$ 199.6	$ 28.2
Commercial paper	107.6	236.1
Total	307.2	264.3
Trade Receivables – Net
Allowance for doubtful receivables	(1.4)	(1.4)
Trade receivables – net	175.2	167.1
Inventories
Finished products	43.1	42.6
Work-in-process	89.8	63.5
Raw materials	55.2	65.0
Operating supplies	6.5	6.5
Total	194.6	177.6
Property, Plant and Equipment – Net
Land and improvements	20.8	21.4
Buildings and leasehold improvements	106.8	104.5
Machinery and equipment	821.0	813.5
Construction in progress	44.0	33.2
Property, plant and equipment – gross	992.6	972.6
Accumulated depreciation	(364.0)	(352.2)
Assets held for sale	2.3	1.6
Property, plant and equipment – net	630.9	622.0
Other Accrued Liabilities
Uncleared cash disbursements	5.7	4.2
Accrued income taxes and taxes payable	10.3	6.2
Accrued annual contribution to Salaried VEBA	0.0	2.9
Accrued interest	2.0	2.3
Short-term environmental accrual	4.7	5.5
Other	34.2	22.9
Total	56.9	44.0
Long-Term Liabilities
Workers’ compensation accruals	28.5	27.7
Long-term environmental accrual	12.3	11.5
Other long-term liabilities	34.5	27.8
Total	75.3	67.0
Excess of Replacement or Current Costs over Stated LIFO Value	$ 1.9	$ 11.9
Workers' Compensation Discount, Percent	1.00%	1.75%
Workers compensation liability	$ 29.0	$ 29.2
Billed
Trade Receivables – Net
Trade receivables, gross	$ 176.6	$ 168.5