Supplemental Balance Sheet Information (Details) - USD ($) $ in Millions	Jun. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Cash and Cash Equivalents
Cash and money market funds	$ 18.1		$ 23.5
Commercial paper	145.9		27.6
Total	164.0		51.1
Trade Receivables – Net
Trade receivables, gross	192.4		166.2
Allowance for doubtful receivables	(1.2)		(1.2)
Trade receivables – net	191.2		165.0
Inventories
Finished products	36.8		63.8
Work-in-process	61.5		78.3
Raw materials	73.7		61.3
Operating supplies	5.2		4.5
Total	177.2	$ 167.2	207.9
Property, Plant and Equipment – Net
Land and improvements	21.1		21.1
Buildings and leasehold improvements	92.9		92.1
Machinery and equipment	719.7		689.1
Construction in progress	36.6		35.1
Property, plant and equipment – gross	870.3		837.4
Accumulated depreciation	(288.0)		(267.9)
Assets held for sale	1.9		1.9
Property, plant and equipment – net	584.2		571.4
Other Accrued Liabilities
Uncleared cash disbursements	6.4		7.3
Accrued income taxes and taxes payable	7.2		6.8
Accrued annual contribution to VEBAs	0.0		15.7
Accrued interest	2.9		2.9
Other	13.4		7.8
Total	29.9	$ 42.0	40.5
Long-Term Liabilities
Workers’ compensation accruals	23.3		22.6
Long-term environmental accrual	14.5		15.8
Other long-term liabilities	24.8		21.6
Total	62.6		60.0
Billed
Trade Receivables – Net
Trade receivables, gross	191.5		165.9
Unbilled
Trade Receivables – Net
Trade receivables, gross	$ 0.9		$ 0.3