Inventories (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Inventories
Retail automotive dealership new vehicles	$ 2,153.0	$ 2,218.6
Retail automotive dealership used vehicles	771.7	719.0
Retail automotive parts, accessories and other	119.1	113.6
Retail commercial truck dealership vehicles and parts	170.3	208.8
Commercial vehicle distribution vehicles and parts	194.1	203.5
Total inventories	3,408.2	3,463.5
Interest credits and advertising assistance	$ 51.6	$ 43.7	$ 39.7