Revenues - Retail Automotive Dealership (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenues
Total revenues	$ 23,179.4	$ 22,785.1	$ 21,386.9
U.S.
Revenues
Total revenues	13,511.8	12,607.8	12,487.2
Retail Automotive Dealership
Revenues
Total revenues	20,615.8	20,849.2	19,824.3
Retail Automotive Dealership | U.S.
Revenues
Total revenues	11,697.6	11,504.3	11,610.1
Retail Automotive Dealership | UK
Revenues
Total revenues	7,559.4	7,961.4	7,048.7
Retail Automotive Dealership | Germany and Italy
Revenues
Total revenues	1,358.8	1,383.5	1,165.5
New vehicle | Retail Automotive Dealership
Revenues
Total revenues	9,329.5	9,666.4	9,678.5
Used vehicle | Retail Automotive Dealership
Revenues
Total revenues	7,241.2	7,252.1	6,386.8
Finance and insurance, net | Retail Automotive Dealership
Revenues
Total revenues	652.1	629.6	581.8
Service and parts | Retail Automotive Dealership
Revenues
Total revenues	2,195.9	2,151.4	2,057.5
Fleet and wholesale | Retail Automotive Dealership
Revenues
Total revenues	$ 1,197.1	$ 1,149.7	$ 1,119.7