Fair Value Measurements (Recurring Measurements) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Derivative assets:
Total derivative assets	$ 0.9	$ 19.8
Pension plan investments	32.5	31.3
Derivative liabilities:
Total derivative liabilities	(7.2)	0.0
Fair Value, Measurements, Recurring
Derivative assets:
Total derivative assets	0.9	19.8
Pension plan investments	32.5	0.1
Total recurring assets at fair value	33.4	19.9
Derivative liabilities:
Total derivative liabilities	(7.2)	0.0
RINS Obligation	(13.0)	(15.8)
Precious metals lease	(5.8)	(5.6)
Other Liabilities, Fair Value Disclosure	(7.4)	(2.7)
Total recurring liabilities at fair value	(33.4)	(24.1)
Fair Value, Measurements, Recurring | Level 1
Derivative assets:
Total derivative assets	0.0	0.0
Pension plan investments	32.5	0.1
Total recurring assets at fair value	32.5	0.1
Derivative liabilities:
Total derivative liabilities	0.0	0.0
RINS Obligation	0.0	0.0
Precious metals lease	(5.8)	(5.6)
Other Liabilities, Fair Value Disclosure	(7.4)	(2.7)
Total recurring liabilities at fair value	(13.2)	(8.3)
Fair Value, Measurements, Recurring | Level 2
Derivative assets:
Total derivative assets	0.0	0.0
Pension plan investments	0.0	0.0
Total recurring assets at fair value	0.0	0.0
Derivative liabilities:
Total derivative liabilities	0.0	0.0
RINS Obligation	(13.0)	(15.8)
Precious metals lease	0.0	0.0
Other Liabilities, Fair Value Disclosure	0.0	0.0
Total recurring liabilities at fair value	(13.0)	(15.8)
Fair Value, Measurements, Recurring | Level 3
Derivative assets:
Total derivative assets	0.9	19.8
Pension plan investments	0.0	0.0
Total recurring assets at fair value	0.9	19.8
Derivative liabilities:
Total derivative liabilities	(7.2)	0.0
RINS Obligation	0.0	0.0
Precious metals lease	0.0	0.0
Other Liabilities, Fair Value Disclosure	0.0	0.0
Total recurring liabilities at fair value	(7.2)	0.0
Fair Value, Measurements, Recurring | Supply and Offtake Agreements
Derivative assets:
Total derivative assets	0.0	(1.5)
Derivative liabilities:
Total derivative liabilities	(7.2)	0.0
Fair Value, Measurements, Recurring | Supply and Offtake Agreements | Level 1
Derivative assets:
Total derivative assets	0.0	0.0
Derivative liabilities:
Total derivative liabilities	0.0	0.0
Fair Value, Measurements, Recurring | Supply and Offtake Agreements | Level 2
Derivative assets:
Total derivative assets	0.0	0.0
Derivative liabilities:
Total derivative liabilities	0.0	0.0
Fair Value, Measurements, Recurring | Supply and Offtake Agreements | Level 3
Derivative assets:
Total derivative assets	0.0	(1.5)
Derivative liabilities:
Total derivative liabilities	(7.2)	0.0
Fair Value, Measurements, Recurring | WCS Crude Oil Basis Swaps
Derivative assets:
Total derivative assets	(1.3)	14.9
Fair Value, Measurements, Recurring | WCS Crude Oil Basis Swaps | Level 1
Derivative assets:
Total derivative assets	0.0	0.0
Fair Value, Measurements, Recurring | WCS Crude Oil Basis Swaps | Level 2
Derivative assets:
Total derivative assets	0.0	0.0
Fair Value, Measurements, Recurring | WCS Crude Oil Basis Swaps | Level 3
Derivative assets:
Total derivative assets	(1.3)	14.9
Fair Value, Measurements, Recurring | WCS Crude Oil Percentage Basis Swaps
Derivative assets:
Total derivative assets	0.0	(6.1)
Fair Value, Measurements, Recurring | WCS Crude Oil Percentage Basis Swaps | Level 1
Derivative assets:
Total derivative assets	0.0	0.0
Fair Value, Measurements, Recurring | WCS Crude Oil Percentage Basis Swaps | Level 2
Derivative assets:
Total derivative assets	0.0	0.0
Fair Value, Measurements, Recurring | WCS Crude Oil Percentage Basis Swaps | Level 3
Derivative assets:
Total derivative assets	0.0	(6.1)
Fair Value, Measurements, Recurring | Midland crude oil basis swap purchases
Derivative assets:
Total derivative assets	0.0	8.1
Fair Value, Measurements, Recurring | Midland crude oil basis swap purchases | Level 1
Derivative assets:
Total derivative assets	0.0	0.0
Fair Value, Measurements, Recurring | Midland crude oil basis swap purchases | Level 2
Derivative assets:
Total derivative assets	0.0	0.0
Fair Value, Measurements, Recurring | Midland crude oil basis swap purchases | Level 3
Derivative assets:
Total derivative assets	0.0	8.1
Fair Value, Measurements, Recurring | Gasoline Crack Spread Swaps
Derivative assets:
Total derivative assets	1.3	0.0
Fair Value, Measurements, Recurring | Gasoline Crack Spread Swaps | Level 1
Derivative assets:
Total derivative assets	0.0	0.0
Fair Value, Measurements, Recurring | Gasoline Crack Spread Swaps | Level 2
Derivative assets:
Total derivative assets	0.0	0.0
Fair Value, Measurements, Recurring | Gasoline Crack Spread Swaps | Level 3
Derivative assets:
Total derivative assets	1.3	0.0
Fair Value, Measurements, Recurring | Diesel Crack Spread Swaps
Derivative assets:
Total derivative assets	0.4	7.4
Fair Value, Measurements, Recurring | Diesel Crack Spread Swaps | Level 1
Derivative assets:
Total derivative assets	0.0	0.0
Fair Value, Measurements, Recurring | Diesel Crack Spread Swaps | Level 2
Derivative assets:
Total derivative assets	0.0	0.0
Fair Value, Measurements, Recurring | Diesel Crack Spread Swaps | Level 3
Derivative assets:
Total derivative assets	0.4	7.4
Fair Value, Measurements, Recurring | Diesel Percent Basis Crack Spread Swaps
Derivative assets:
Total derivative assets	0.0	(6.0)
Fair Value, Measurements, Recurring | Diesel Percent Basis Crack Spread Swaps | Level 1
Derivative assets:
Total derivative assets	0.0	0.0
Fair Value, Measurements, Recurring | Diesel Percent Basis Crack Spread Swaps | Level 2
Derivative assets:
Total derivative assets	0.0	0.0
Fair Value, Measurements, Recurring | Diesel Percent Basis Crack Spread Swaps | Level 3
Derivative assets:
Total derivative assets	0.0	(6.0)
Fair Value, Measurements, Recurring | 2-1-1 Crack Spread Swap
Derivative assets:
Total derivative assets	0.5	0.0
Fair Value, Measurements, Recurring | 2-1-1 Crack Spread Swap | Level 1
Derivative assets:
Total derivative assets	0.0	0.0
Fair Value, Measurements, Recurring | 2-1-1 Crack Spread Swap | Level 2
Derivative assets:
Total derivative assets	0.0	0.0
Fair Value, Measurements, Recurring | 2-1-1 Crack Spread Swap | Level 3
Derivative assets:
Total derivative assets	$ 0.5	$ 0.0