Revenues - Retail Commercial Truck Dealership (Details) - Retail Commercial Truck Dealership - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Revenues
Total revenues	$ 338.8		$ 631.2
New vehicle
Revenues
Total revenues	210.7		381.1
Used vehicle
Revenues
Total revenues	27.3		53.8
Finance and insurance, net
Revenues
Total revenues	3.6		6.8
Service and parts
Revenues
Total revenues	92.2		182.6
Wholesale
Revenues
Total revenues	$ 5.0		$ 6.9
Without Adoption of ASC 606
Revenues
Total revenues		$ 228.5		$ 440.2
Without Adoption of ASC 606 | New vehicle
Revenues
Total revenues		116.5		227.2
Without Adoption of ASC 606 | Used vehicle
Revenues
Total revenues		23.2		42.2
Without Adoption of ASC 606 | Finance and insurance, net
Revenues
Total revenues		2.3		4.5
Without Adoption of ASC 606 | Service and parts
Revenues
Total revenues		83.3		161.3
Without Adoption of ASC 606 | Wholesale
Revenues
Total revenues		$ 3.2		$ 5.0