Revenues - Retail Automotive Dealership (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Revenues
Total revenues	$ 7,447.8	$ 6,920.7	$ 22,255.3	$ 20,803.0
Retail automotive dealership
Revenues
Total revenues	6,325.4	5,757.8	19,031.2	17,784.3	$ 23,700.0
Retail automotive dealership | U.S.
Revenues
Total revenues	3,595.9	3,400.8	10,511.1	10,188.3
Retail automotive dealership | U.K.
Revenues
Total revenues	2,306.8	2,002.0	7,180.7	6,461.3
Retail automotive dealership | Germany, Italy, and Japan
Revenues
Total revenues	422.7	355.0	1,339.4	1,134.7
New vehicle | Retail automotive dealership
Revenues
Total revenues	2,742.7	2,395.2	8,284.1	7,286.7
Used vehicle | Retail automotive dealership
Revenues
Total revenues	2,322.1	2,208.8	6,949.5	7,019.5
Finance and insurance, net | Retail automotive dealership
Revenues
Total revenues	210.1	208.1	631.0	646.8
Service and parts | Retail automotive dealership
Revenues
Total revenues	685.2	609.8	2,053.4	1,793.0
Fleet and wholesale | Retail automotive dealership
Revenues
Total revenues	$ 365.3	$ 335.9	$ 1,113.2	$ 1,038.3