Revenues - Retail Automotive Dealership (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2026	Sep. 30, 2025
Revenues
Total revenues	$ 8,415.6	$ 8,053.0	$ 24,791.9	$ 24,039.3
Retail automotive dealership
Revenues
Total revenues	7,025.4	6,927.8	21,293.5	20,734.1
Retail automotive dealership | U.S.
Revenues
Total revenues	4,208.7	4,221.6	12,457.1	12,427.2
Retail automotive dealership | U.K.
Revenues
Total revenues	2,182.9	2,087.4	6,755.3	6,496.4
Retail automotive dealership | Germany, Italy, Japan, and Australia
Revenues
Total revenues	633.8	618.8	2,081.1	1,810.5
Retail automotive dealership | New vehicle
Revenues
Total revenues	3,213.6	3,198.1	9,669.7	9,634.1
Retail automotive dealership | Used vehicle
Revenues
Total revenues	2,383.7	2,299.0	7,285.0	6,822.5
Retail automotive dealership | Finance and insurance, net
Revenues
Total revenues	197.6	203.1	610.9	616.7
Retail automotive dealership | Service and parts
Revenues
Total revenues	869.8	854.0	2,600.8	2,533.1
Retail automotive dealership | Fleet and wholesale
Revenues
Total revenues	$ 360.7	$ 373.6	$ 1,127.1	$ 1,127.7