Revenues - Retail Automotive Dealership (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Revenues
Total revenues	$ 7,590.8	$ 7,447.8	$ 22,735.3	$ 22,255.3
Retail automotive dealership
Revenues
Total revenues	6,340.7	6,325.4	19,434.1	19,031.2
Retail automotive dealership | U.S.
Revenues
Total revenues	3,584.3	3,595.9	10,712.0	10,511.1
Retail automotive dealership | U.K.
Revenues
Total revenues	2,265.7	2,306.8	7,211.2	7,180.7
Retail automotive dealership | Germany, Italy, Japan, and Australia
Revenues
Total revenues	490.7	422.7	1,510.9	1,339.4
New vehicle | Retail automotive dealership
Revenues
Total revenues	2,890.2	2,742.7	8,688.6	8,284.1
Used vehicle | Retail automotive dealership
Revenues
Total revenues	2,123.9	2,322.1	6,735.9	6,949.5
Finance and insurance, net | Retail automotive dealership
Revenues
Total revenues	193.1	210.1	607.8	631.0
Service and parts | Retail automotive dealership
Revenues
Total revenues	778.0	685.2	2,276.9	2,053.4
Fleet and wholesale | Retail automotive dealership
Revenues
Total revenues	$ 355.5	$ 365.3	$ 1,124.9	$ 1,113.2