Supplemental Balance Sheet Information (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Cash and Cash Equivalents.
Cash and money market funds	$ 57.7	$ 107.9
Commercial paper	111.8	165.5
Total	169.5	273.4	49.8	135.6
Trade Receivables.
Billed trade receivables	120.2	124.4
Unbilled trade receivables — Note 1	0.4	0.2
Trade receivables, gross	120.6	124.6
Allowance for doubtful receivables	(0.8)	(0.8)
Trade receivables, net	119.8	123.8
Inventories.
Finished products	72.5	59.9
Work-in-process	75.9	55.5
Raw materials	47.2	53.9
Operating supplies and repairs and maintenance parts	18.8	16.7
Total	214.4	186.0
Prepaid Expenses and Other Current Assets.
Current derivative assets — Notes 11 and 12	2.0	3.0
Current deferred tax assets	36.7	59.5
Current portion of option premiums paid — Notes 11 and 12	0	0.1
Short-term restricted cash	0.3	1.3
Prepaid taxes	0	2.1
Prepaid expenses	5.2	4.1
Total	44.2	70.1
Property, Plant, and Equipment - Net.
Land and improvements	22.6	22.6
Buildings and leasehold improvements	53.0	50.9
Machinery and equipment	425.6	400.4
Construction in progress	66.0	20.8
Active property, plant, and equipment, gross	567.2	494.7
Accumulated depreciation	(137.9)	(111.4)
Active property, plant, and equipment, net	429.3	383.3
Idled equipment	0	1.0
Property, plant, and equipment, net	429.3	384.3
Other Assets.
Derivative assets — Notes 11 and 12	79.8	55.5
Restricted cash	9.3	10.0
Long-term income tax receivable	0	2.9
Deferred financing costs	8.9	11.7
Deferred compensation plan assets	6.5	5.6
Other	0.3	0.3
Total	104.8	86.0
Other Accrued Liabilities.
Current derivative liabilities — Notes 11 and 12	1.8	3.1
Current portion of option premiums received — Notes 11 and 12	0	0.1
Uncleared cash disbursement	9.6	4.7
Accrued income taxes and taxes payable	4.3	3.1
Accrued annual VEBA contribution	16.0	20.0
Short-term environmental accrual — Note 10	2.8	3.0
Accrued interest	3.7	3.7
Short-term deferred revenue — Note 1	0	6.7
Other	6.6	7.4
Total	44.8	51.8
Long-term Liabilities.
Derivative liabilities — Notes 11 and 12	84.3	63.5
Income tax liabilities	5.0	15.1
Workers’ compensation accruals	23.3	24.0
Long-term environmental accrual — Note 10	20.0	18.7
Long-term asset retirement obligations	4.0	3.8
Deferred compensation liability	7.0	5.8
Long-term capital leases	0.1	0.2
Other long-term liabilities	2.7	3.4
Total	146.4	134.5
Long-term Debt. — Note 3
Senior notes	225.0	225.0
Cash convertible senior notes	163.5	155.3
Total	$ 388.5	$ 380.3