Supplemental Balance Sheet Information (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Cash and Cash Equivalents
Cash and money market funds	$ 23.5	$ 37.9
Commercial paper	27.6	17.3
Total	51.1	55.2
Trade Receivables - Net
Billed trade receivables	165.9	138.2
Unbilled trade receivables	0.3	0.3
Trade receivables, gross	166.2	138.5
Allowance for doubtful receivables	(1.2)	(0.8)
Trade receivables - net	165.0	137.7
Inventories
Finished products	63.8	73.8
Work-in-process	78.3	71.7
Raw materials	61.3	51.1
Operating supplies	4.5	5.0
Total	207.9	201.6
Property, Plant and Equipment - Net
Land and improvements	21.1	22.7
Buildings and leasehold improvements	92.1	88.6
Machinery and equipment	689.1	615.1
Construction in progress	35.1	34.8
Property, plant and equipment - gross	837.4	761.2
Accumulated depreciation	(267.9)	(230.6)
Assets held for sale	1.9	0.3
Property, plant and equipment - net	571.4	530.9
Other Accrued Liabilities
Uncleared cash disbursements	7.3	5.8
Accrued income taxes and taxes payable	6.8	4.3
Accrued annual contribution to VEBAs – Note 4	15.7	20.0
Accrued interest	2.9	2.9
Other	7.8	7.1
Total	40.5	40.1
Long-Term Liabilities
Workers’ compensation accruals	22.6	25.0
Long-term environmental accrual – Note 9	15.8	15.8
Long-term portion of contingent contribution to Union VEBA	0.0	12.8
Other long-term liabilities	21.6	19.6
Total	$ 60.0	$ 73.2