Revenues (Disaggregation of Revenue) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Disaggregation of Revenue [Line Items]
Total revenues	$ 3,184.8	$ 3,116.4
Total petroleum product sales
Disaggregation of Revenue [Line Items]
Total revenues	2,480.2	2,499.8
Petroleum product sales (at retail)
Disaggregation of Revenue [Line Items]
Total revenues	2,246.2	2,238.7
Petroleum product sales (at wholesale)
Disaggregation of Revenue [Line Items]
Total revenues	234.0	261.1
Merchandise sales
Disaggregation of Revenue [Line Items]
Total revenues	687.5	606.2
RINs
Disaggregation of Revenue [Line Items]
Total revenues	15.5	9.1
Other revenues
Disaggregation of Revenue [Line Items]
Total revenues	1.6	1.3
Operating Segments | Marketing
Disaggregation of Revenue [Line Items]
Total revenues	3,184.7	3,116.3
Operating Segments | Marketing | Total petroleum product sales
Disaggregation of Revenue [Line Items]
Total revenues	2,480.2	2,499.8
Operating Segments | Marketing | Petroleum product sales (at retail)
Disaggregation of Revenue [Line Items]
Total revenues	2,246.2	2,238.7
Operating Segments | Marketing | Petroleum product sales (at wholesale)
Disaggregation of Revenue [Line Items]
Total revenues	234.0	261.1
Operating Segments | Marketing | Merchandise sales
Disaggregation of Revenue [Line Items]
Total revenues	687.5	606.2
Operating Segments | Marketing | RINs
Disaggregation of Revenue [Line Items]
Total revenues	15.5	9.1
Operating Segments | Marketing | Other revenues
Disaggregation of Revenue [Line Items]
Total revenues	1.5	1.2
Corporate and other assets
Disaggregation of Revenue [Line Items]
Total revenues	0.1	0.1
Corporate and other assets | Total petroleum product sales
Disaggregation of Revenue [Line Items]
Total revenues	0.0	0.0
Corporate and other assets | Petroleum product sales (at retail)
Disaggregation of Revenue [Line Items]
Total revenues	0.0	0.0
Corporate and other assets | Petroleum product sales (at wholesale)
Disaggregation of Revenue [Line Items]
Total revenues	0.0	0.0
Corporate and other assets | Merchandise sales
Disaggregation of Revenue [Line Items]
Total revenues	0.0	0.0
Corporate and other assets | RINs
Disaggregation of Revenue [Line Items]
Total revenues	0.0	0.0
Corporate and other assets | Other revenues
Disaggregation of Revenue [Line Items]
Total revenues	$ 0.1	$ 0.1