Supplemental Balance Sheet Information (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012	Dec. 31, 2011
Cash and Cash Equivalents.
Cash and money market funds	$ 78.1	$ 107.9
Commercial paper	203.6	165.5
Total	281.7	273.4	317.8	49.8
Trade Receivables.
Billed trade receivables	119.1	124.4
Unbilled trade receivables	4.4	0.2
Trade receivables, gross	123.5	124.6
Allowance for doubtful receivables	(0.8)	(0.8)
Trade receivables, net	122.7	123.8
Inventories.
Finished products	61.7	59.9
Work-in-process	69.1	55.5
Raw materials	54.5	53.9
Operating supplies and repair and maintenance parts	17.6	16.7
Total	202.9	186.0
Prepaid Expenses and Other Current Assets.
Current derivative assets – Notes 9 and 10	1.2	3.0
Current deferred tax assets	59.5	59.5
Current portion of option premiums paid – Notes 9 and 10	0.1	0.1
Short-term restricted cash	1.3	1.3
Prepaid taxes	4.0	2.1
Prepaid expenses	4.0	4.1
Total	70.1	70.1
Property, Plant and Equipment - Net.
Land and improvements	22.6	22.6
Buildings and leasehold improvements	51.8	50.9
Machinery and equipment	406.5	400.4
Construction in progress	41.1	20.8
Active property, plant and equipment, gross	522.0	494.7
Accumulated depreciation	(124.7)	(111.4)
Active property, plant and equipment, net	397.3	383.3
Idled equipment	1.0	1.0
Total	398.3	384.3
Other Assets.
Derivative assets – Notes 9 and 10	52.5	55.5
Restricted cash	9.3	10.0
Long-term income tax receivable	0	2.9
Deferred financing costs	10.3	11.7
Available for sale securities	6.0	5.6
Other	0.4	0.3
Total	78.5	86.0
Other Accrued Liabilities.
Current derivative liabilities – Notes 9 and 10	6.0	3.1
Current portion of option premiums received – Notes 9 and 10	0.1	0.1
Uncleared cash disbursement	11.8	4.7
Accrued income taxes and taxes payable	5.7	3.1
Accrued annual VEBA contribution	0	20.0
Short-term environmental accrual – Note 8	4.6	3.0
Accrued interest	3.7	3.7
Short-term deferred revenue	3.2	6.7
Other	4.8	7.4
Total	39.9	51.8
Long-term Liabilities.
Derivative liabilities – Notes 9 and 10	61.2	63.5
Income tax liabilities	11.7	15.1
Workers’ compensation accruals	23.2	24.0
Long-term environmental accrual – Note 8	17.1	18.7
Long-term asset retirement obligations	4.0	3.8
Deferred compensation liability	6.3	5.8
Long-term capital lease	0.2	0.2
Other long-term liabilities	3.3	3.4
Total	127.0	134.5
Long-term Debt. — Note 3
Senior notes	225.0	225.0
Cash convertible senior notes	159.3	155.3
Total	$ 384.3	$ 380.3