Revenues - Retail Commercial Truck Dealership (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenues
Total revenues	$ 23,179.4	$ 22,785.1	$ 21,386.9
Retail Commercial Truck Dealership
Revenues
Total revenues	2,050.5	1,374.5	1,048.0
New vehicle | Retail Commercial Truck Dealership
Revenues
Total revenues	1,347.2	866.9	613.2
Used vehicle | Retail Commercial Truck Dealership
Revenues
Total revenues	117.0	112.0	89.4
Finance and insurance, net | Retail Commercial Truck Dealership
Revenues
Total revenues	12.4	11.9	8.9
Service and parts | Retail Commercial Truck Dealership
Revenues
Total revenues	503.3	364.5	325.6
Other | Retail Commercial Truck Dealership
Revenues
Total revenues	$ 70.6	$ 19.2	$ 10.9