Revenues - Retail Automotive Dealership (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Revenues
Total revenues	$ 5,971.6	$ 5,967.6	$ 14,631.8	$ 17,287.8
Retail Automotive Dealership
Revenues
Total revenues	5,258.0	5,155.4	12,828.1	15,442.9
Retail Automotive Dealership | U.S.
Revenues
Total revenues	2,780.7	2,995.5	7,288.4	8,624.1
Retail Automotive Dealership | UK
Revenues
Total revenues	2,105.5	1,859.6	4,608.7	5,827.7
Retail Automotive Dealership | Germany and Italy
Revenues
Total revenues	371.8	300.3	931.0	991.1
New vehicle | Retail Automotive Dealership
Revenues
Total revenues	2,350.6	2,332.3	5,599.8	6,873.9
Used vehicle | Retail Automotive Dealership
Revenues
Total revenues	1,954.1	1,824.5	4,739.8	5,529.2
Finance and insurance, net | Retail Automotive Dealership
Revenues
Total revenues	174.4	166.0	415.8	491.5
Service and parts | Retail Automotive Dealership
Revenues
Total revenues	521.8	543.5	1,380.3	1,654.0
Fleet and wholesale | Retail Automotive Dealership
Revenues
Total revenues	$ 257.1	$ 289.1	$ 692.4	$ 894.3