Revenues - Retail Commercial Truck Dealership (Details) - Retail Commercial Truck Dealership - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenues
Total revenues	$ 385.3		$ 1,016.5
New vehicle
Revenues
Total revenues	249.4		630.5
Used vehicle
Revenues
Total revenues	32.5		86.3
Finance and insurance, net
Revenues
Total revenues	2.9		9.0
Service and parts
Revenues
Total revenues	93.1		275.7
Other
Revenues
Total revenues	$ 7.4		$ 15.0
Without Adoption of ASC 606
Revenues
Total revenues		$ 299.6		$ 739.8
Without Adoption of ASC 606 | New vehicle
Revenues
Total revenues		184.3		411.5
Without Adoption of ASC 606 | Used vehicle
Revenues
Total revenues		25.7		67.9
Without Adoption of ASC 606 | Finance and insurance, net
Revenues
Total revenues		2.1		6.6
Without Adoption of ASC 606 | Service and parts
Revenues
Total revenues		83.3		244.6
Without Adoption of ASC 606 | Other
Revenues
Total revenues		$ 4.2		$ 9.2