Fair Value Measurements - Schedule of Assets and Liabilities (Details) - Recurring - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Fair value measurements
Cash equivalents	$ 15.7	$ 15.7
Other current assets (investments)	4.8	0.1
Total Assets	33.8	60.5
Total Liabilities	(21.1)	(2.9)
Other derivative agreements
Fair value measurements
Other current assets (other derivative agreements)	13.3	44.7
Other current liabilities (other derivative agreements and interest rate swaps)	(0.3)	(0.1)
Interest rate swaps
Fair value measurements
Other current liabilities (other derivative agreements and interest rate swaps)		(0.1)
Biofuels blending obligation
Fair value measurements
Other current liabilities (biofuel blending obligations)	(20.8)	(2.7)
Level 1
Fair value measurements
Cash equivalents	15.7	15.7
Other current assets (investments)	4.8	0.1
Total Assets	20.5	15.8
Total Liabilities	0.0	0.0
Level 1 | Other derivative agreements
Fair value measurements
Other current assets (other derivative agreements)	0.0	0.0
Other current liabilities (other derivative agreements and interest rate swaps)	0.0	0.0
Level 1 | Interest rate swaps
Fair value measurements
Other current liabilities (other derivative agreements and interest rate swaps)		0.0
Level 1 | Biofuels blending obligation
Fair value measurements
Other current liabilities (biofuel blending obligations)	0.0	0.0
Level 2
Fair value measurements
Cash equivalents	0.0	0.0
Other current assets (investments)	0.0	0.0
Total Assets	13.3	44.7
Total Liabilities	(21.1)	(2.9)
Level 2 | Other derivative agreements
Fair value measurements
Other current assets (other derivative agreements)	13.3	44.7
Other current liabilities (other derivative agreements and interest rate swaps)	(0.3)	(0.1)
Level 2 | Interest rate swaps
Fair value measurements
Other current liabilities (other derivative agreements and interest rate swaps)		(0.1)
Level 2 | Biofuels blending obligation
Fair value measurements
Other current liabilities (biofuel blending obligations)	(20.8)	(2.7)
Level 3
Fair value measurements
Cash equivalents	0.0	0.0
Other current assets (investments)	0.0	0.0
Total Assets	0.0	0.0
Total Liabilities	0.0	0.0
Level 3 | Other derivative agreements
Fair value measurements
Other current assets (other derivative agreements)	0.0	0.0
Other current liabilities (other derivative agreements and interest rate swaps)	0.0	0.0
Level 3 | Interest rate swaps
Fair value measurements
Other current liabilities (other derivative agreements and interest rate swaps)		0.0
Level 3 | Biofuels blending obligation
Fair value measurements
Other current liabilities (biofuel blending obligations)	$ 0.0	$ 0.0