Inventories (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Inventories
Retail automotive dealership new vehicles	$ 1,938.7		$ 1,938.7		$ 2,346.2
Retail automotive dealership used vehicles	815.4		815.4		1,080.8
Retail automotive parts, accessories and other	117.4		117.4		141.5
Retail commercial truck dealership vehicles and parts	339.4		339.4		465.2
Commercial vehicle distribution vehicles, parts and engines	215.0		215.0		227.0
Total inventories	3,425.9		3,425.9		$ 4,260.7
Interest credits and advertising assistance	$ 12.7	$ 12.8	$ 24.2	$ 24.9