Supplemental Balance Sheet Information (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012	Dec. 31, 2011
Cash and Cash Equivalents.
Cash and money market funds	$ 82.9	$ 107.9
Commercial paper	165.1	165.5
Total	248.0	273.4	77.3	49.8
Trade Receivables.
Billed trade receivables	140.1	124.4
Unbilled trade receivables	2.5	0.2
Trade receivables, gross	142.6	124.6
Allowance for doubtful receivables	(0.8)	(0.8)
Trade receivables, net	141.8	123.8
Inventories.
Finished products	61.2	59.9
Work-in-process	68.0	55.5
Raw materials	52.8	53.9
Operating supplies and repair and maintenance parts	17.3	16.7
Total	199.3	186.0
Prepaid Expenses and Other Current Assets.
Current derivative assets – Notes 8 and 9	1.5	3.0
Current deferred tax assets	59.5	59.5
Current portion of option premiums paid – Notes 8 and 9	0.1	0.1
Short-term restricted cash	1.3	1.3
Prepaid taxes	4.7	2.1
Prepaid expenses	3.9	4.1
Total	71.0	70.1
Property, Plant and Equipment - Net.
Land and improvements	22.6	22.6
Buildings and leasehold improvements	51.7	50.9
Machinery and equipment	403.5	400.4
Construction in progress	25.6	20.8
Active property, plant and equipment, gross	503.4	494.7
Accumulated depreciation	(118.0)	(111.4)
Active property, plant and equipment, net	385.4	383.3
Idled equipment	1.0	1.0
Total	386.4	384.3
Other Assets.
Derivative assets – Notes 8 and 9	61.8	55.5
Restricted cash	10.0	10.0
Long-term income tax receivable	0	2.9
Deferred financing costs	11.0	11.7
Available for sale securities	5.8	5.6
Other	0.2	0.3
Total	88.8	86.0
Other Accrued Liabilities.
Current derivative liabilities – Notes 8 and 9	3.1	3.1
Current portion of option premiums received – Notes 8 and 9	0.1	0.1
Accrued book overdraft (uncleared cash disbursement)	5.7	4.7
Accrued income taxes and taxes payable	5.4	3.1
Accrued annual VEBA contribution	0	20.0
Short-term environmental accrual – Note 7	4.7	3.0
Accrued interest	10.3	3.7
Short-term deferred revenue	4.6	6.7
Other	4.5	7.4
Total	38.4	51.8
Long-term Liabilities.
Derivative liabilities – Notes 8 and 9	68.8	63.5
Income tax liabilities	11.9	15.1
Workers’ compensation accruals	23.5	24.0
Long-term environmental accrual – Note 7	17.3	18.7
Long-term asset retirement obligations	3.9	3.8
Deferred compensation liability	6.2	5.8
Long-term capital lease	0.2	0.2
Other long-term liabilities	3.4	3.4
Total	135.2	134.5
Long-term Debt. — Note 3
Senior notes	225.0	225.0
Cash convertible senior notes	157.3	155.3
Total	$ 382.3	$ 380.3