Revenues - Retail Automotive Dealership (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Revenues
Total revenues	$ 7,696.7	$ 7,468.5	$ 15,144.5	$ 14,807.5
Retail automotive dealership
Revenues
Total revenues	6,615.4	6,406.0	13,093.4	12,705.8
Retail automotive dealership | U.S.
Revenues
Total revenues	3,712.7	3,537.0	7,127.7	6,915.2
Retail automotive dealership | U.K.
Revenues
Total revenues	2,399.0	2,401.5	4,945.5	4,873.9
Retail automotive dealership | Germany, Italy, Japan, and Australia
Revenues
Total revenues	503.7	467.5	1,020.2	916.7
New vehicle | Retail automotive dealership
Revenues
Total revenues	2,995.8	2,820.1	5,798.4	5,541.4
Used vehicle | Retail automotive dealership
Revenues
Total revenues	2,275.8	2,330.3	4,612.0	4,627.4
Finance and insurance, net | Retail automotive dealership
Revenues
Total revenues	208.7	214.1	414.7	420.9
Service and parts | Retail automotive dealership
Revenues
Total revenues	752.8	685.2	1,498.9	1,368.2
Fleet and wholesale | Retail automotive dealership
Revenues
Total revenues	$ 382.3	$ 356.3	$ 769.4	$ 747.9