Revenues (Disaggregation of Revenue) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Revenue	$ 3,460.2	$ 3,657.6	$ 3,800.4	$ 3,116.4	$ 3,501.7	$ 3,788.0	$ 3,829.0	$ 3,244.2	$ 14,034.6	$ 14,362.9	$ 12,826.6
Merchandise sales
Disaggregation of Revenue [Line Items]
Revenue									2,620.1	2,423.0	2,372.7
Operating Segment
Disaggregation of Revenue [Line Items]
Revenue									14,034.3	75.2	12,826.2
Operating Segment | Petroleum product sales (at retail)
Disaggregation of Revenue [Line Items]
Revenue									10,184.0	10,459.2	9,041.5
Operating Segment | Petroleum product sales (at wholesale)
Disaggregation of Revenue [Line Items]
Revenue									1,189.8	1,399.2	1,246.4
Operating Segment | Total petroleum product sales
Disaggregation of Revenue [Line Items]
Revenue									11,373.8	11,858.4	10,287.9
Operating Segment | Merchandise sales
Disaggregation of Revenue [Line Items]
Revenue									2,620.1	2,423.0	2,372.6
Operating Segment | Renewable Identification Numbers (RINs) sales
Disaggregation of Revenue [Line Items]
Revenue									34.8		160.3
Operating Segment | Other
Disaggregation of Revenue [Line Items]
Revenue									5.6		5.4
Operating Segment | Marketing
Disaggregation of Revenue [Line Items]
Revenue										14,362.3
Operating Segment | Marketing | Other
Disaggregation of Revenue [Line Items]
Revenue										5.7
Corporate and Other Assets
Disaggregation of Revenue [Line Items]
Revenue									$ 0.3	$ 0.6	$ 0.4