Fair Value Measurements - Summary of Recurring Assets and Liabilities Measured at Fair Value (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring [Line Items]
Derivative Credit Risk Valuation Adjustment, Derivative Assets	$ 0.0	$ 0.0
Derivative Credit Risk Valuation Adjustment, Derivative Liabilities	0.0	0.0
Assets:
Total derivative assets	(24.1)	(0.9)
Derivative liabilities:
Total derivative liabilities	0.0	7.2
Fair Value, Measurements, Recurring
Assets:
Total derivative assets	(24.1)	(0.9)
Pension plan investments	31.9	32.5
Assets, Fair Value Disclosure	56.0	33.4
Derivative liabilities:
Total derivative liabilities	0.0	7.2
RINs Obligation	(58.8)	(13.0)
Precious metals lease	(5.0)	(5.8)
Liability Awards	(8.4)	(7.4)
Total recurring liabilities at fair value	(72.2)	(33.4)
Fair Value, Measurements, Recurring | Level 1
Assets:
Total derivative assets	0.0	0.0
Pension plan investments	31.9	32.5
Assets, Fair Value Disclosure	31.9	32.5
Derivative liabilities:
Total derivative liabilities	0.0	0.0
RINs Obligation	0.0	0.0
Precious metals lease	(5.0)	(5.8)
Liability Awards	(8.4)	(7.4)
Total recurring liabilities at fair value	(13.4)	(13.2)
Fair Value, Measurements, Recurring | Level 2
Assets:
Total derivative assets	0.0	0.0
Pension plan investments	0.0	0.0
Assets, Fair Value Disclosure	0.0	0.0
Derivative liabilities:
Total derivative liabilities	0.0	0.0
RINs Obligation	(58.8)	(13.0)
Precious metals lease	0.0	0.0
Liability Awards	0.0	0.0
Total recurring liabilities at fair value	(58.8)	(13.0)
Fair Value, Measurements, Recurring | Level 3
Assets:
Total derivative assets	(24.1)	(0.9)
Pension plan investments	0.0	0.0
Assets, Fair Value Disclosure	24.1	0.9
Derivative liabilities:
Total derivative liabilities	0.0	7.2
RINs Obligation	0.0	0.0
Precious metals lease	0.0	0.0
Liability Awards	0.0	0.0
Total recurring liabilities at fair value	0.0	(7.2)
Natural Gas Swaps [Member] | Fair Value, Measurements, Recurring
Assets:
Total derivative assets	0.2	0.0
Natural Gas Swaps [Member] | Fair Value, Measurements, Recurring | Level 1
Assets:
Total derivative assets	0.0	0.0
Natural Gas Swaps [Member] | Fair Value, Measurements, Recurring | Level 2
Assets:
Total derivative assets	0.0	0.0
Natural Gas Swaps [Member] | Fair Value, Measurements, Recurring | Level 3
Assets:
Total derivative assets	0.2	0.0
Inventory Financing Obligations | Fair Value, Measurements, Recurring
Assets:
Total derivative assets	4.4	0.0
Inventory Financing Obligations | Fair Value, Measurements, Recurring | Level 1
Assets:
Total derivative assets	0.0	0.0
Inventory Financing Obligations | Fair Value, Measurements, Recurring | Level 2
Assets:
Total derivative assets	0.0	0.0
Inventory Financing Obligations | Fair Value, Measurements, Recurring | Level 3
Assets:
Total derivative assets	4.4	0.0
Diesel crack spread swaps | Fair Value, Measurements, Recurring
Assets:
Total derivative assets	(9.5)	(0.4)
Diesel crack spread swaps | Fair Value, Measurements, Recurring | Level 1
Assets:
Total derivative assets	0.0	0.0
Diesel crack spread swaps | Fair Value, Measurements, Recurring | Level 2
Assets:
Total derivative assets	0.0	0.0
Diesel crack spread swaps | Fair Value, Measurements, Recurring | Level 3
Assets:
Total derivative assets	(9.5)	(0.4)
Diesel-MEH crack spread swap [Member] [Domain] | Fair Value, Measurements, Recurring
Assets:
Total derivative assets	(0.9)	0.0
Diesel-MEH crack spread swap [Member] [Domain] | Fair Value, Measurements, Recurring | Level 1
Assets:
Total derivative assets	0.0	0.0
Diesel-MEH crack spread swap [Member] [Domain] | Fair Value, Measurements, Recurring | Level 2
Assets:
Total derivative assets	0.0	0.0
Diesel-MEH crack spread swap [Member] [Domain] | Fair Value, Measurements, Recurring | Level 3
Assets:
Total derivative assets	(0.9)	0.0
WCS crude oil basis swaps | Fair Value, Measurements, Recurring
Assets:
Total derivative assets	(4.9)	1.3
WCS crude oil basis swaps | Fair Value, Measurements, Recurring | Level 1
Assets:
Total derivative assets	0.0	0.0
WCS crude oil basis swaps | Fair Value, Measurements, Recurring | Level 2
Assets:
Total derivative assets	0.0	0.0
WCS crude oil basis swaps | Fair Value, Measurements, Recurring | Level 3
Assets:
Total derivative assets	(4.9)	1.3
2-1-1- Crack Spread Swap | Fair Value, Measurements, Recurring
Assets:
Total derivative assets	0.0	(0.5)
2-1-1- Crack Spread Swap | Fair Value, Measurements, Recurring | Level 1
Assets:
Total derivative assets	0.0	0.0
2-1-1- Crack Spread Swap | Fair Value, Measurements, Recurring | Level 2
Assets:
Total derivative assets	0.0	0.0
2-1-1- Crack Spread Swap | Fair Value, Measurements, Recurring | Level 3
Assets:
Total derivative assets	0.0	(0.5)
Gasoline Crack Spread Swaps | Fair Value, Measurements, Recurring
Assets:
Total derivative assets	(4.6)	(1.3)
Gasoline Crack Spread Swaps | Fair Value, Measurements, Recurring | Level 1
Assets:
Total derivative assets	0.0	0.0
Gasoline Crack Spread Swaps | Fair Value, Measurements, Recurring | Level 2
Assets:
Total derivative assets	0.0	0.0
Gasoline Crack Spread Swaps | Fair Value, Measurements, Recurring | Level 3
Assets:
Total derivative assets	(4.6)	(1.3)
Inventory Financing Obligations | Fair Value, Measurements, Recurring
Derivative liabilities:
Total derivative liabilities	0.0	7.2
Inventory Financing Obligations | Fair Value, Measurements, Recurring | Level 1
Derivative liabilities:
Total derivative liabilities	0.0	0.0
Inventory Financing Obligations | Fair Value, Measurements, Recurring | Level 2
Derivative liabilities:
Total derivative liabilities	0.0	0.0
Inventory Financing Obligations | Fair Value, Measurements, Recurring | Level 3
Derivative liabilities:
Total derivative liabilities	$ 0.0	$ (7.2)