Revenues - Retail Automotive Dealership (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Revenues
Total revenues	$ 5,009.1	$ 5,564.4
Retail Automotive Dealership
Revenues
Total revenues	4,416.6	5,091.2	$ 20,600.0
Retail Automotive Dealership | U.S.
Revenues
Total revenues	2,453.9	2,722.8
Retail Automotive Dealership | UK
Revenues
Total revenues	1,665.4	2,039.9
Retail Automotive Dealership | Germany and Italy
Revenues
Total revenues	297.3	328.5
New vehicle | Retail Automotive Dealership
Revenues
Total revenues	1,864.5	2,231.2
Used vehicle | Retail Automotive Dealership
Revenues
Total revenues	1,619.6	1,852.0
Finance and insurance, net | Retail Automotive Dealership
Revenues
Total revenues	144.4	160.0
Service and parts | Retail Automotive Dealership
Revenues
Total revenues	513.3	559.8
Fleet and wholesale | Retail Automotive Dealership
Revenues
Total revenues	$ 274.8	$ 288.2