Fair Value Measurements, Level 3 Fair Value Input Reconciliation Table (Details) (Derivative, Midwest premium swap contracts, USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2015
Derivative \| Midwest premium swap contracts
Reconciliation of activity for financial instruments classified as Level 3:
Balance at December 31, 2014	$ 1.0
Total realized/unrealized (losses) included in:
Cost of goods sold excluding depreciation and amortization and other items and Unrealized losses (gains) on derivative instruments	(2.5)
Transactions involving Level 3 derivative contracts:
Purchases	(1.7)
Sales	0
Issuances	0
Settlements	(0.4)
Transactions involving Level 3 derivatives — net	(2.1)
Transfers in and (or) out of Level 3 valuation hierarchy	0
Balance at March 31, 2015	(3.6)
Total (losses) included in Unrealized losses (gains) on derivative instruments, attributable to the change in unrealized gains/losses relating to derivative contracts held at March 31, 2015:	$ (4.0)

Fair Value Assets Measured on Recurring Basis Change in Unrealized Gain (Loss) Included in Earnings.

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Amount of gain (loss) recognized in the income statement of financial instrument classified as a derivative asset (liability) after deduction of derivative liability (asset), measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of issuances of financial instrument classified as a derivative asset (liability) after deduction of derivative liability (asset), measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of purchases of financial instrument classified as a derivative asset (liability) after deduction of derivative liability (asset), measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of purchases, (sales), issuances and (settlements) of financial instrument classified as a derivative asset (liability) after deduction of derivative liability (asset), measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of sales of financial instrument classified as a derivative asset (liability) after deduction of derivative liability (asset), measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of settlements of financial instrument classified as a derivative asset (liability) after deduction of derivative liability, measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of transfers of financial instrument classified as a derivative asset (liability) after deduction of derivative liability (asset) into (out of) level 3 of the fair value hierarchy.

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