Inventories - Schedule of Inventory (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Inventory [Line Items]
Total inventories	$ 4,705.1	$ 4,640.2
Retail automotive dealership new vehicles
Inventory [Line Items]
Total inventories	2,204.4	2,345.7
Retail automotive dealership used vehicles
Inventory [Line Items]
Total inventories	1,238.5	1,119.2
Retail automotive parts, accessories, and other
Inventory [Line Items]
Total inventories	181.0	167.8
Retail commercial truck dealership vehicles and parts
Inventory [Line Items]
Total inventories	531.5	518.4
Commercial vehicle distribution vehicles, parts, and engines
Inventory [Line Items]
Total inventories	$ 549.7	$ 489.1