Fair Value Measurements (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash collateral	$ 23.9	$ 11.1
Interest Rate Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash collateral		2.0
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total net fair value of derivative assets	308.1	403.7
Derivative Liability	(369.5)	(368.6)
Net assets (liabilities)	(61.4)	35.1
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total net fair value of derivative assets	0.0	0.0
Derivative Liability	0.0	0.0
Net assets (liabilities)	0.0	0.0
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total net fair value of derivative assets	308.1	403.7
Derivative Liability	(369.5)	(368.6)
Net assets (liabilities)	(61.4)	35.1
Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total net fair value of derivative assets	0.0	0.0
Derivative Liability	0.0	0.0
Net assets (liabilities)	0.0	0.0
Fair Value, Measurements, Recurring [Member] | OTC commodity swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total net fair value of derivative assets	295.2	389.6
Derivative Liability	(347.5)	(353.3)
Fair Value, Measurements, Recurring [Member] | OTC commodity swaps [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total net fair value of derivative assets	0.0	0.0
Derivative Liability	0.0	0.0
Fair Value, Measurements, Recurring [Member] | OTC commodity swaps [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total net fair value of derivative assets	295.2	389.6
Derivative Liability	(347.5)	(353.3)
Fair Value, Measurements, Recurring [Member] | OTC commodity swaps [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total net fair value of derivative assets	0.0	0.0
Derivative Liability	0.0	0.0
Fair Value, Measurements, Recurring [Member] | Interest Rate Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Liability		(0.9)
Fair Value, Measurements, Recurring [Member] | Interest Rate Contract [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Liability		0.0
Fair Value, Measurements, Recurring [Member] | Interest Rate Contract [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Liability		(0.9)
Fair Value, Measurements, Recurring [Member] | Interest Rate Contract [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Liability		0.0
Fair Value, Measurements, Recurring [Member] | RINs Obligation [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total net fair value of derivative assets	12.9	14.1
Derivative Liability	(22.0)	(14.4)
Fair Value, Measurements, Recurring [Member] | RINs Obligation [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total net fair value of derivative assets	0.0	0.0
Derivative Liability	0.0	0.0
Fair Value, Measurements, Recurring [Member] | RINs Obligation [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total net fair value of derivative assets	12.9	14.1
Derivative Liability	(22.0)	(14.4)
Fair Value, Measurements, Recurring [Member] | RINs Obligation [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total net fair value of derivative assets	0.0	0.0
Derivative Liability	$ 0.0	$ 0.0