Derivatives (Offsetting Derivative Assets) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 3.2	$ 33.5
Derivative Asset, Collateral, Obligation to Return Cash, Offset	(2.3)	(13.7)
Derivative Asset	0.9	19.8
Not Designated as Hedging Instrument \| Specialty Product \| Midland crude oil basis swap purchases
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset	0.0	1.0
Derivative Asset, Collateral, Obligation to Return Cash, Offset	0.0	0.0
Derivative Asset	0.0	1.0
Not Designated as Hedging Instrument \| Fuel Product \| Midland crude oil basis swap purchases
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset	0.0	7.1
Derivative Asset, Collateral, Obligation to Return Cash, Offset	0.0	0.0
Derivative Asset	0.0	7.1
Not Designated as Hedging Instrument \| Fuel Product \| Supply and Offtake Agreements
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset	0.0	1.5
Derivative Asset, Collateral, Obligation to Return Cash, Offset	0.0	0.0
Derivative Asset	0.0	1.5
Not Designated as Hedging Instrument \| Fuel Product \| WCS Crude Oil Basis Swaps
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset	0.0	16.5
Derivative Asset, Collateral, Obligation to Return Cash, Offset	(1.3)	(1.6)
Derivative Asset	(1.3)	14.9
Not Designated as Hedging Instrument \| Fuel Product \| WCS Crude Oil Percentage Basis Swaps
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset	0.0	0.0
Derivative Asset, Collateral, Obligation to Return Cash, Offset	0.0	(6.1)
Derivative Asset	0.0	(6.1)
Not Designated as Hedging Instrument \| Fuel Product \| Gasoline Crack Spread Swaps
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset	1.8	0.0
Derivative Asset, Collateral, Obligation to Return Cash, Offset	(0.5)	0.0
Derivative Asset	1.3	0.0
Not Designated as Hedging Instrument \| Fuel Product \| Diesel Crack Spread Swaps
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset	0.9	7.4
Derivative Asset, Collateral, Obligation to Return Cash, Offset	(0.5)	0.0
Derivative Asset	0.4	7.4
Not Designated as Hedging Instrument \| Fuel Product \| Diesel Percent Basis Crack Spread Swaps
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset	0.0	0.0
Derivative Asset, Collateral, Obligation to Return Cash, Offset	0.0	(6.0)
Derivative Asset	0.0	(6.0)
Not Designated as Hedging Instrument \| Fuel Product \| 2-1-1 Crack Spread Swap
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset	0.5	0.0
Derivative Asset, Collateral, Obligation to Return Cash, Offset	0.0	0.0
Derivative Asset	$ 0.5	$ 0.0

Amount of obligation to return cash collateral under master netting arrangements offset against derivative assets.

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