Inventories (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Inventories
Retail automotive dealership new vehicles	$ 2,252.4		$ 2,252.4		$ 2,397.0
Retail automotive dealership used vehicles	988.9		988.9		1,060.8
Retail automotive parts, accessories and other	126.6		126.6		140.8
Retail commercial truck dealership vehicles and parts	462.9		462.9		207.9
Commercial vehicle distribution vehicles, parts and engines	213.1		213.1		233.6
Total inventories	4,043.9		4,043.9		$ 4,040.1
Interest credits and advertising assistance	$ 12.8	$ 15.1	$ 37.7	$ 40.7