Revenues - Retail Automotive Dealership (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Revenues
Total revenues	$ 7,695.3	$ 7,590.8	$ 22,962.1	$ 22,735.3
Retail automotive dealership
Revenues
Total revenues	6,570.1	6,340.7	19,656.9	19,434.1
Retail automotive dealership | U.S.
Revenues
Total revenues	3,863.9	3,584.3	11,350.0	10,712.0
Retail automotive dealership | U.K.
Revenues
Total revenues	2,087.4	2,265.7	6,496.4	7,211.2
Retail automotive dealership | Germany, Italy, Japan, and Australia
Revenues
Total revenues	618.8	490.7	1,810.5	1,510.9
New vehicle | Retail automotive dealership
Revenues
Total revenues	2,961.1	2,890.2	8,925.0	8,688.6
Used vehicle | Retail automotive dealership
Revenues
Total revenues	2,242.8	2,123.9	6,643.8	6,735.9
Finance and insurance, net | Retail automotive dealership
Revenues
Total revenues	195.9	193.1	594.6	607.8
Service and parts | Retail automotive dealership
Revenues
Total revenues	818.3	778.0	2,424.3	2,276.9
Fleet and wholesale | Retail automotive dealership
Revenues
Total revenues	$ 352.0	$ 355.5	$ 1,069.2	$ 1,124.9