Supplemental Balance Sheet Information (Details) - USD ($) $ in Millions	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Cash and Cash Equivalents
Cash and money market funds	$ 22.9		$ 23.5
Commercial paper	102.7		27.6
Total	125.6		51.1
Trade Receivables - Net
Billed trade receivables	179.5		165.9
Unbilled trade receivables	1.1		0.3
Trade receivables, gross	180.6		166.2
Allowance for doubtful receivables	(0.8)		(1.2)
Trade receivables - net	179.8		165.0
Inventories
Finished products	48.0		63.8
Work-in-process	85.6		78.3
Raw materials	75.0		61.3
Operating supplies	6.5		4.5
Total	215.1	$ 167.2	207.9
Property, Plant and Equipment - Net
Land and improvements	21.4		21.1
Buildings and leasehold improvements	97.0		92.1
Machinery and equipment	755.6		689.1
Construction in progress	43.6		35.1
Property, plant and equipment - gross	917.6		837.4
Accumulated depreciation	(307.4)		(267.9)
Assets held for sale	1.6		1.9
Property, plant and equipment - net	611.8		571.4
Other Accrued Liabilities
Uncleared cash disbursements	4.8		7.3
Accrued income taxes and taxes payable	6.5		6.8
Accrued annual contribution to VEBAs – Note 4	2.1		15.7
Accrued interest	2.9		2.9
Other	27.7		7.8
Total	44.0	$ 42.0	40.5
Long-Term Liabilities
Workers’ compensation accruals	24.6		22.6
Long-term environmental accrual – Note 9	14.3		15.8
Other long-term liabilities	27.5		21.6
Total	$ 66.4		$ 60.0