Revenues - Retail Automotive Dealership (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Revenues
Total revenues	$ 3,651.1	$ 5,755.8	$ 8,660.2	$ 11,320.2
Retail Automotive Dealership
Revenues
Total revenues	3,153.5	5,196.3	7,570.1	10,287.5
Retail Automotive Dealership | U.S.
Revenues
Total revenues	2,053.8	2,905.9	4,507.7	5,628.6
Retail Automotive Dealership | UK
Revenues
Total revenues	837.8	1,928.2	2,503.2	3,968.1
Retail Automotive Dealership | Germany and Italy
Revenues
Total revenues	261.9	362.2	559.2	690.8
New vehicle | Retail Automotive Dealership
Revenues
Total revenues	1,384.7	2,310.4	3,249.2	4,541.6
Used vehicle | Retail Automotive Dealership
Revenues
Total revenues	1,166.0	1,852.7	2,785.6	3,704.7
Finance and insurance, net | Retail Automotive Dealership
Revenues
Total revenues	97.1	165.5	241.5	325.5
Service and parts | Retail Automotive Dealership
Revenues
Total revenues	345.2	550.7	858.5	1,110.5
Fleet and wholesale | Retail Automotive Dealership
Revenues
Total revenues	$ 160.5	$ 317.0	$ 435.3	$ 605.2