Revenues - Retail Commercial Truck Dealership (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Revenues
Total revenues	$ 6,987.5	$ 3,651.1	$ 12,761.3	$ 8,660.2
Retail commercial truck dealership
Revenues
Total revenues	625.3	399.2	1,060.0	890.6
New vehicle | Retail commercial truck dealership
Revenues
Total revenues	399.2	235.5	646.7	553.8
Used vehicle | Retail commercial truck dealership
Revenues
Total revenues	59.0	36.9	110.0	71.5
Finance and insurance, net | Retail commercial truck dealership
Revenues
Total revenues	3.8	3.2	6.9	6.4
Service and parts | Retail commercial truck dealership
Revenues
Total revenues	157.3	111.6	281.9	236.0
Other | Retail commercial truck dealership
Revenues
Total revenues	$ 6.0	$ 12.0	$ 14.5	$ 22.9