Supplemental Balance Sheet Information (Details) - USD ($) $ in Millions		Dec. 31, 2016	Dec. 31, 2015
Cash and Cash Equivalents
Cash and money market funds		$ 37.9	$ 40.3
Commercial paper		17.3	32.2
Total		55.2	72.5
Trade Receivables - Net
Billed trade receivables		138.2	116.8
Unbilled trade receivables		0.3	0.7
Trade receivables, gross		138.5	117.5
Allowance for doubtful receivables		(0.8)	(0.8)
Trade receivables - net		137.7	116.7
Inventories
Finished products		73.8	79.5
Work-in-process		71.7	63.6
Raw materials		51.1	53.4
Operating supplies		5.0	23.1
Total		201.6	219.6
Prepaid Expenses and Other Current Assets
Current replacement parts		7.6	0.0
Current derivative assets — Notes 10 and 11		5.0	1.5
Current deferred tax assets – Note 1		0.0	49.6
Prepaid insurance		1.9	1.9
Short-term restricted cash		0.3	0.3
Other		3.7	3.4
Total	[1]	18.5	56.7
Property, Plant and Equipment - Net
Land and improvements		22.7	22.7
Buildings and leasehold improvements		88.6	71.8
Machinery and equipment		615.1	549.0
Construction in progress		34.8	48.5
Property, plant and equipment - gross		761.2	692.0
Accumulated depreciation		(230.6)	(196.9)
Assets held for sale		0.3	0.3
Property, plant and equipment - net		530.9	495.4
Other Assets
Restricted cash		12.2	10.9
Long-term replacement parts		11.2	0.0
Debt issuance costs on Revolving Credit Facility		1.0	1.3
Deferred compensation plan assets		8.2	7.3
Derivative assets – Note 10		0.8	0.1
Total	[1]	33.4	19.6
Other Accrued Liabilities
Current derivative liabilities – Note 10		0.8	14.1
Uncleared cash disbursements		5.8	8.0
Accrued income taxes and taxes payable		4.3	3.1
Accrued annual contribution to VEBAs – Note 6		20.0	19.6
Short-term environmental accrual – Note 9		1.4	1.6
Accrued interest		2.9	1.5
Short-term deferred revenue		0.2	1.2
Other		4.5	3.6
Total		39.9	52.7
Long-Term Liabilities
Derivative liabilities – Note 10		1.0	2.1
Income tax liabilities		0.9	0.7
Workers’ compensation accruals		25.0	21.7
Long-term environmental accrual – Note 9		15.8	17.0
Long-term asset retirement obligations		5.3	4.8
Long-term deferred revenue – Note 1		0.1	0.3
Deferred compensation liability		8.2	7.7
Long-term capital leases		0.2	0.1
Long-term portion of contingent contribution to Union VEBA		12.8	29.9
Other long-term liabilities		3.9	3.2
Total		$ 73.2	$ 87.5

[1] See Note 1 for discussion of our adoption of ASU 2015-03 and ASU 2015-17 (as defined in Note 1).