Revenues (Disaggregation of Revenue) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Disaggregation of Revenue [Line Items]
Revenue	$ 2,839.0	$ 3,657.6	$ 8,403.4	$ 10,574.4
Total petroleum product sales
Disaggregation of Revenue [Line Items]
Revenue	2,056.0	2,965.5	6,125.1	8,595.0
Petroleum product sales (at retail)
Disaggregation of Revenue [Line Items]
Revenue	1,867.8	2,660.8	5,558.8	7,717.7
Petroleum product sales (at wholesale)
Disaggregation of Revenue [Line Items]
Revenue	188.2	304.7	566.3	877.3
Merchandise sales
Disaggregation of Revenue [Line Items]
Revenue	756.8	681.1	2,211.4	1,946.1
RINs
Disaggregation of Revenue [Line Items]
Revenue	25.2	8.6	63.3	28.6
Other revenues
Disaggregation of Revenue [Line Items]
Revenue	1.0	2.4	3.6	4.7
Operating Segments | Marketing
Disaggregation of Revenue [Line Items]
Revenue	2,839.1	3,657.6	8,403.4	10,574.3
Operating Segments | Marketing | Total petroleum product sales
Disaggregation of Revenue [Line Items]
Revenue	2,056.0	2,965.5	6,125.1	8,595.0
Operating Segments | Marketing | Petroleum product sales (at retail)
Disaggregation of Revenue [Line Items]
Revenue	1,867.8	2,660.8	5,558.8	7,717.7
Operating Segments | Marketing | Petroleum product sales (at wholesale)
Disaggregation of Revenue [Line Items]
Revenue	188.2	304.7	566.3	877.3
Operating Segments | Marketing | Merchandise sales
Disaggregation of Revenue [Line Items]
Revenue	756.8	681.1	2,211.4	1,946.1
Operating Segments | Marketing | RINs
Disaggregation of Revenue [Line Items]
Revenue	25.2	8.6	63.3	28.6
Operating Segments | Marketing | Other revenues
Disaggregation of Revenue [Line Items]
Revenue	1.1	2.4	3.6	4.6
Corporate and other assets
Disaggregation of Revenue [Line Items]
Revenue	(0.1)	0.0	0.0	0.1
Corporate and other assets | Total petroleum product sales
Disaggregation of Revenue [Line Items]
Revenue	0.0	0.0	0.0	0.0
Corporate and other assets | Petroleum product sales (at retail)
Disaggregation of Revenue [Line Items]
Revenue	0.0	0.0	0.0	0.0
Corporate and other assets | Petroleum product sales (at wholesale)
Disaggregation of Revenue [Line Items]
Revenue	0.0	0.0	0.0	0.0
Corporate and other assets | Merchandise sales
Disaggregation of Revenue [Line Items]
Revenue	0.0	0.0	0.0	0.0
Corporate and other assets | RINs
Disaggregation of Revenue [Line Items]
Revenue	0.0	0.0	0.0	0.0
Corporate and other assets | Other revenues
Disaggregation of Revenue [Line Items]
Revenue	$ (0.1)	$ 0.0	$ 0.0	$ 0.1