Revenues - Retail Commercial Truck Dealership (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Revenues
Total revenues	$ 5,967.6	$ 5,658.6	$ 17,287.8	$ 17,345.8
Retail Commercial Truck Dealership
Revenues
Total revenues	692.3	385.3	1,451.4	1,016.5
New vehicle | Retail Commercial Truck Dealership
Revenues
Total revenues	476.2	249.4	979.6	630.5
Used vehicle | Retail Commercial Truck Dealership
Revenues
Total revenues	36.1	32.5	87.8	86.3
Finance and insurance, net | Retail Commercial Truck Dealership
Revenues
Total revenues	3.1	2.9	9.0	9.0
Service and parts | Retail Commercial Truck Dealership
Revenues
Total revenues	154.6	93.1	340.7	275.7
Other | Retail Commercial Truck Dealership
Revenues
Total revenues	$ 22.3	$ 7.4	$ 34.3	$ 15.0