Supplemental Balance Sheet Information (Details) - USD ($) $ in Millions	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Cash and Cash Equivalents
Cash and money market funds	$ 17.3		$ 23.5
Commercial paper	117.7		27.6
Total	135.0		51.1
Trade Receivables – Net
Trade receivables, gross	186.5		166.2
Allowance for doubtful receivables	(1.2)		(1.2)
Trade receivables – net	185.3		165.0
Inventories
Finished products	40.5		63.8
Work-in-process	63.3		78.3
Raw materials	68.2		61.3
Operating supplies	4.8		4.5
Total	176.8	$ 167.2	207.9
Property, Plant and Equipment – Net
Land and improvements	21.1		21.1
Buildings and leasehold improvements	91.9		92.1
Machinery and equipment	698.6		689.1
Construction in progress	42.9		35.1
Property, plant and equipment – gross	854.5		837.4
Accumulated depreciation	(277.7)		(267.9)
Assets held for sale	1.9		1.9
Property, plant and equipment – net	578.7		571.4
Other Accrued Liabilities
Uncleared cash disbursements	4.7		7.3
Accrued income taxes and taxes payable	10.8		6.8
Accrued annual contribution to VEBAs	0.0		15.7
Accrued interest	8.4		2.9
Other	11.7		7.8
Total	35.6	$ 42.0	40.5
Long-Term Liabilities
Workers’ compensation accruals	23.2		22.6
Long-term environmental accrual	14.7		15.8
Other long-term liabilities	23.4		21.6
Total	61.3		60.0
Billed
Trade Receivables – Net
Trade receivables, gross	186.1		165.9
Unbilled
Trade Receivables – Net
Trade receivables, gross	$ 0.4		$ 0.3