Fair Value Measurements (Details) (Recurring, USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Fair value measurements
Cash equivalents	$ 69.0	$ 81.0
Marketable Securities	76.6us-gaap_MarketableSecurities
Total Assets	192.9us-gaap_AssetsFairValueDisclosure	82.0us-gaap_AssetsFairValueDisclosure
Total Liabilities	(50.6)us-gaap_LiabilitiesFairValueDisclosure	(35.2)us-gaap_LiabilitiesFairValueDisclosure
Commodity swaps
Fair value measurements
Other current assets	25.0	0.9
Other long-term assets	22.3	0.1
Other current liabilities		(15.3)
Other long-term liabilities		(1.8)
Interest rate swap
Fair value measurements
Other current liabilities	(0.8)	(0.9)
Other long-term liabilities	(0.2)	(1.0)
Biofuels blending obligation
Fair value measurements
Other current liabilities (biofuel blending obligation)	(49.6)	(16.2)
Level 1
Fair value measurements
Cash equivalents	69.0	81.0
Marketable Securities	73.9
Total Assets	142.9	81.0
Total Liabilities	0	0
Level 1 \| Commodity swaps
Fair value measurements
Other current assets	0	0
Other long-term assets	0	0
Other current liabilities		0
Other long-term liabilities		0
Level 1 \| Interest rate swap
Fair value measurements
Other current liabilities	0	0
Other long-term liabilities	0	0
Level 1 \| Biofuels blending obligation
Fair value measurements
Other current liabilities (biofuel blending obligation)	0	0
Level 2
Fair value measurements
Cash equivalents	0	0
Marketable Securities	2.7
Total Assets	50.0	1.0
Total Liabilities	(50.6)	(35.2)
Level 2 \| Commodity swaps
Fair value measurements
Other current assets	25.0	0.9
Other long-term assets	22.3	0.1
Other current liabilities		(15.3)
Other long-term liabilities		(1.8)
Level 2 \| Interest rate swap
Fair value measurements
Other current liabilities	(0.8)	(0.9)
Other long-term liabilities	(0.2)	(1.0)
Level 2 \| Biofuels blending obligation
Fair value measurements
Other current liabilities (biofuel blending obligation)	(49.6)	(16.2)
Level 3
Fair value measurements
Cash equivalents	0	0
Marketable Securities	0
Total Assets	0	0
Total Liabilities	0	0
Level 3 \| Commodity swaps
Fair value measurements
Other current assets	0	0
Other long-term assets	0	0
Other current liabilities		0
Other long-term liabilities		0
Level 3 \| Interest rate swap
Fair value measurements
Other current liabilities	0	0
Other long-term liabilities	0	0
Level 3 \| Biofuels blending obligation
Fair value measurements
Other current liabilities (biofuel blending obligation)	$ 0	$ 0

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Fair value of financial and nonfinancial obligations.

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Total debt and equity financial instruments including: (1) securities held-to-maturity, (2) trading securities, and (3) securities available-for-sale.

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