Segment Information - Revenues and Segment Income by Reportable Segment (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Segment Reporting Information
Revenues	$ 7,863.6	$ 7,953.8
Cost of sales	6,564.2	6,632.4
Selling, general, and administrative expenses:
Personnel expenses	566.6	557.3
Advertising expenses	31.1	30.9
Rent & related expenses	116.5	109.2
Other expenses	251.4	254.0
Depreciation	44.8	40.6
Floor plan interest expense	38.1	42.0
Other interest expense	28.4	22.5
Equity in earnings of affiliates	40.8	33.3
Segment income	323.7	350.5
Gain on sale of dealership	60.4	52.3
Retail Automotive
Segment Reporting Information
Revenues	6,967.1	6,918.6
Cost of sales	5,842.1	5,782.4
Selling, general, and administrative expenses:
Personnel expenses	483.4	472.6
Advertising expenses	29.8	29.7
Rent & related expenses	105.3	99.0
Other expenses	228.2	232.6
Depreciation	38.8	35.3
Floor plan interest expense	34.5	36.0
Other interest expense	26.5	18.0
Equity in earnings of affiliates	0.0	0.3
Segment income	238.9	265.6
Retail Commercial Truck
Segment Reporting Information
Revenues	694.6	823.7
Cost of sales	566.4	682.7
Selling, general, and administrative expenses:
Personnel expenses	63.2	65.9
Advertising expenses	0.7	0.9
Rent & related expenses	6.8	6.6
Other expenses	14.4	14.9
Depreciation	4.4	3.9
Floor plan interest expense	2.3	3.7
Other interest expense	0.0	0.0
Equity in earnings of affiliates	0.0	0.0
Segment income	36.4	45.1
Other
Segment Reporting Information
Revenues	201.9	211.5
Cost of sales	155.7	167.3
Selling, general, and administrative expenses:
Personnel expenses	20.0	18.8
Advertising expenses	0.6	0.3
Rent & related expenses	4.4	3.6
Other expenses	8.8	6.5
Depreciation	1.6	1.4
Floor plan interest expense	1.3	2.3
Other interest expense	1.9	4.5
Equity in earnings of affiliates	0.0	0.0
Segment income	7.6	6.8
Non-Automotive Investments
Segment Reporting Information
Revenues	0.0	0.0
Cost of sales	0.0	0.0
Selling, general, and administrative expenses:
Personnel expenses	0.0	0.0
Advertising expenses	0.0	0.0
Rent & related expenses	0.0	0.0
Other expenses	0.0	0.0
Depreciation	0.0	0.0
Floor plan interest expense	0.0	0.0
Other interest expense	0.0	0.0
Equity in earnings of affiliates	40.8	33.0
Segment income	$ 40.8	$ 33.0