Supplemental Balance Sheet Information (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012	Dec. 31, 2011
Cash and Cash Equivalents.
Cash and money market funds	$ 89.5	$ 107.9
Commercial paper	135.1	165.5
Total	224.6	273.4	255.6	49.8
Trade Receivables.
Trade receivables, gross	122.9	124.6
Allowance for doubtful receivables	(0.8)	(0.8)
Trade receivables, net	122.1	123.8
Inventories.
Finished products	68.6	59.9
Work-in-process	70.1	55.5
Raw materials	50.9	53.9
Operating supplies and repair and maintenance parts	18.3	16.7
Total	207.9	186.0
Prepaid Expenses and Other Current Assets.
Current derivative assets – Notes 9 and 10	0.7	3.0
Current deferred tax assets	59.5	59.5
Current portion of option premiums paid – Notes 9 and 10	0	0.1
Short-term restricted cash	1.3	1.3
Prepaid taxes	2.4	2.1
Prepaid expenses	3.7	4.1
Total	67.6	70.1
Property, Plant and Equipment - Net.
Land and improvements	22.6	22.6
Buildings and leasehold improvements	52.5	50.9
Machinery and equipment	416.5	400.4
Construction in progress	50.1	20.8
Active property, plant and equipment, gross	541.7	494.7
Accumulated depreciation	(131.0)	(111.4)
Active property, plant and equipment, net	410.7	383.3
Idled equipment	1.0	1.0
Total	411.7	384.3
Other Assets.
Derivative assets – Notes 9 and 10	83.6	55.5
Restricted cash	9.3	10.0
Long-term income tax receivable	0	2.9
Deferred financing costs	9.6	11.7
Deferred compensation plan assets	6.3	5.6
Other	0.3	0.3
Total	109.1	86.0
Other Accrued Liabilities.
Current derivative liabilities – Notes 9 and 10	4.0	3.1
Current portion of option premiums received – Notes 9 and 10	0.1	0.1
Uncleared cash disbursement	7.8	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	5.3	3.0
Accrued interest	10.3	3.7
Short-term deferred revenue	1.9	6.7
Other	5.8	7.4
Total	40.9	51.8
Long-term Liabilities.
Derivative liabilities – Notes 9 and 10	90.7	63.5
Income tax liabilities	9.8	15.1
Workers’ compensation accruals	22.9	24.0
Long-term environmental accrual – Note 8	16.5	18.7
Long-term asset retirement obligations	3.9	3.8
Deferred compensation liability	6.7	5.8
Long-term capital lease	0.1	0.2
Other long-term liabilities	3.4	3.4
Total	154.0	134.5
Long-term Debt. — Note 3
Senior notes	225.0	225.0
Cash convertible senior notes	161.4	155.3
Total	386.4	380.3
Billed
Trade Receivables.
Trade receivables, gross	116.5	124.4
Unbilled
Trade Receivables.
Trade receivables, gross	$ 6.4	$ 0.2