Inventories (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Inventories
Retail automotive dealership new vehicles	$ 1,553.6		$ 1,553.6		$ 2,346.2
Retail automotive dealership used vehicles	995.7		995.7		1,080.8
Retail automotive parts, accessories and other	115.9		115.9		141.5
Retail commercial truck dealership vehicles and parts	316.5		316.5		465.2
Commercial vehicle distribution vehicles, parts and engines	228.0		228.0		227.0
Total inventories	3,209.7		3,209.7		$ 4,260.7
Interest credits and advertising assistance	$ 13.6	$ 12.8	$ 37.8	$ 37.7