Inventories (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Inventories
Retail automotive dealership new vehicles	$ 869.1	$ 1,810.9
Retail automotive dealership used vehicles	1,420.0	1,019.7
Retail automotive parts, accessories, and other	126.4	117.2
Retail commercial truck dealership vehicles and parts	436.7	223.1
Commercial vehicle distribution vehicles, parts, and engines	276.8	254.7
Total inventories	3,129.0	3,425.6
Interest credits and advertising assistance	$ 63.7	$ 52.6	$ 51.6