Revenues - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Revenues
Total revenues	$ 29,527.4	$ 27,814.8	$ 25,554.7
Revenue recognized from unearned revenue	$ 220.7
Commercial vehicle distribution and other
Revenues
Payment period	30 days
Total revenues	$ 634.0	578.8	575.7
Retail automotive dealership
Revenues
Total revenues	25,209.1	23,694.7	22,513.3
Retail automotive dealership | U.K.
Revenues
Total revenues	$ 9,240.4	8,443.4	7,984.1
Dealership 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	$ 265.2	241.0	242.8
Service and parts | Retail automotive dealership
Revenues
Total revenues	$ 2,734.3	2,426.7	2,165.6
Finance and insurance, net | Retail Automotive and Retail Commercial Truck Dealership
Revenues
Payment period	30 days
Aggregate reserves relating to chargeback activity	$ 42.7	38.4
Finance and insurance, net | Retail automotive dealership
Revenues
Total revenues	$ 838.6	$ 848.1	$ 780.5