Revenues - Retail Automotive Dealership (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
Revenues
Total revenues	$ 8,512.7	$ 8,032.5	$ 16,376.3	$ 15,986.3
Retail automotive dealership
Revenues
Total revenues	7,301.0	6,887.7	14,268.1	13,806.3
Retail automotive dealership \| U.S.
Revenues
Total revenues	4,367.8	4,165.3	8,248.4	8,205.6
Retail automotive dealership \| U.K.
Revenues
Total revenues	2,224.7	2,085.8	4,572.4	4,409.0
Retail automotive dealership \| Germany, Italy, Japan, and Australia
Revenues
Total revenues	708.5	636.6	1,447.3	1,191.7
Retail automotive dealership \| New vehicle
Revenues
Total revenues	3,375.4	3,188.1	6,456.1	6,436.1
Retail automotive dealership \| Used vehicle
Revenues
Total revenues	2,471.9	2,259.4	4,901.3	4,523.5
Retail automotive dealership \| Finance and insurance, net
Revenues
Total revenues	211.0	208.2	413.3	413.6
Retail automotive dealership \| Service and parts
Revenues
Total revenues	867.1	853.4	1,731.0	1,679.0
Retail automotive dealership \| Fleet and wholesale
Revenues
Total revenues	$ 375.6	$ 378.6	$ 766.4	$ 754.1