Revenues - Narrative (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
Revenue recognized from unearned revenue									$ 212.7
Commercial vehicle distribution and other
Revenues
Payment period									45 days
Total revenues									$ 922.6	777.9	634.0
Vehicle Sales | Retail Automotive and Retail Commercial Truck Dealership
Revenues
Payment period									30 days
Service and parts | Retail Automotive and Retail Commercial Truck Dealership
Revenues
Payment period									30 days
Service and parts | Commercial vehicle distribution and other
Revenues
Total revenues									$ 281.6	274.1	$ 265.2
Finance and insurance, net | Retail Automotive and Retail Commercial Truck Dealership
Revenues
Payment period									30 days
Aggregate reserves relating to chargeback activity	$ 55.3				$ 51.6				$ 55.3	$ 51.6