Supplemental Balance Sheet Information (Details) - USD ($) $ in Millions	Sep. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Cash and Cash Equivalents
Cash and money market funds	$ 23.2		$ 23.5
Commercial paper	71.1		27.6
Total	94.3		51.1
Trade Receivables – Net
Trade receivables, gross	195.7		166.2
Allowance for doubtful receivables	(1.2)		(1.2)
Trade receivables – net	194.5		165.0
Inventories
Finished products	41.4		63.8
Work-in-process	73.3		78.3
Raw materials	76.2		61.3
Operating supplies	5.3		4.5
Total	196.2	$ 167.2	207.9
Property, Plant and Equipment – Net
Land and improvements	21.4		21.1
Buildings and leasehold improvements	96.4		92.1
Machinery and equipment	736.3		689.1
Construction in progress	38.1		35.1
Property, plant and equipment – gross	892.2		837.4
Accumulated depreciation	(298.4)		(267.9)
Assets held for sale	1.6		1.9
Property, plant and equipment – net	595.4		571.4
Other Accrued Liabilities
Uncleared cash disbursements	5.6		7.3
Accrued income taxes and taxes payable	8.2		6.8
Accrued annual contribution to VEBAs	0.0		15.7
Accrued interest	8.4		2.9
Other	14.8		7.8
Total	37.0	$ 42.0	40.5
Long-Term Liabilities
Workers’ compensation accruals	24.5		22.6
Long-term environmental accrual	14.4		15.8
Other long-term liabilities	25.8		21.6
Total	64.7		60.0
Billed
Trade Receivables – Net
Trade receivables, gross	194.2		165.9
Unbilled
Trade Receivables – Net
Trade receivables, gross	$ 1.5		$ 0.3