Revenues - Retail Automotive Dealership (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2025	Sep. 30, 2025	Jun. 30, 2025	Mar. 31, 2025	Dec. 31, 2024	Sep. 30, 2024	Jun. 30, 2024	Mar. 31, 2024	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Revenues
Total revenues	$ 7,769.2	$ 8,053.0	$ 8,032.5	$ 7,953.8	$ 8,077.6	$ 7,929.5	$ 8,065.0	$ 7,792.7	$ 31,808.5	$ 31,864.8	$ 30,916.5
U.S.
Revenues
Total revenues									19,578.8	19,124.7	18,575.6
U.K.
Revenues
Total revenues									8,334.4	9,322.0	9,240.4
Retail automotive dealership
Revenues
Total revenues									27,474.6	27,565.8	26,598.2
Retail automotive dealership | U.S.
Revenues
Total revenues									16,643.0	16,187.2	15,549.6
Retail automotive dealership | U.K.
Revenues
Total revenues									8,334.4	9,322.0	9,240.4
Retail automotive dealership | Germany, Italy, Japan, and Australia
Revenues
Total revenues									2,497.2	2,056.6	1,808.2
New vehicle | Retail automotive dealership
Revenues
Total revenues									12,855.4	12,960.6	12,186.6
Used vehicle | Retail automotive dealership
Revenues
Total revenues									8,941.1	9,040.0	9,167.8
Finance and insurance, net | Retail automotive dealership
Revenues
Total revenues									816.5	841.0	869.9
Service and parts | Retail automotive dealership
Revenues
Total revenues									3,377.9	3,182.8	2,863.2
Fleet and wholesale | Retail automotive dealership
Revenues
Total revenues									$ 1,483.7	$ 1,541.4	$ 1,510.7