Inventories - Schedule of Inventory (Details) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Inventory [Line Items]
Total inventories	$ 4,822.4	$ 4,293.1
Retail automotive dealership new vehicles
Inventory [Line Items]
Total inventories	2,353.0	1,951.3
Retail automotive dealership used vehicles
Inventory [Line Items]
Total inventories	1,154.1	1,186.3
Retail automotive parts, accessories, and other
Inventory [Line Items]
Total inventories	169.2	156.2
Retail commercial truck dealership vehicles and parts
Inventory [Line Items]
Total inventories	596.6	543.7
Commercial vehicle distribution vehicles, parts, and engines
Inventory [Line Items]
Total inventories	$ 549.5	$ 455.6