Segment Information - Revenues and Segment Income by Reportable Segment (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Segment Reporting Information
Revenues	$ 7,604.5	$ 7,447.8
Cost of sales	6,335.5	6,202.6
Selling, general, and administrative expenses:
Personnel expenses	531.5	521.1
Advertising expenses	30.0	33.1
Rent & related expenses	105.3	103.5
Other expenses	246.8	222.1
Depreciation	39.9	37.8
Floor plan interest expense	41.5	44.8
Other interest expense	22.5	21.3
Equity in earnings of affiliates	33.3	33.3
Segment income	337.1	294.8
Gain on sale of dealership	52.3
Retail Automotive
Segment Reporting Information
Revenues	6,569.3	6,478.0
Cost of sales	5,485.5	5,420.8
Selling, general, and administrative expenses:
Personnel expenses	446.8	437.4
Advertising expenses	28.8	32.0
Rent & related expenses	95.1	93.4
Other expenses	225.4	204.1
Depreciation	34.6	32.9
Floor plan interest expense	35.5	38.8
Other interest expense	18.0	21.2
Equity in earnings of affiliates	0.3	1.0
Segment income	252.2	198.4
Retail Commercial Truck
Segment Reporting Information
Revenues	823.7	791.8
Cost of sales	682.7	647.0
Selling, general, and administrative expenses:
Personnel expenses	65.9	66.2
Advertising expenses	0.9	0.7
Rent & related expenses	6.6	6.5
Other expenses	14.9	13.3
Depreciation	3.9	3.6
Floor plan interest expense	3.7	4.0
Other interest expense	0.0	0.0
Equity in earnings of affiliates	0.0	0.0
Segment income	45.1	50.5
Other
Segment Reporting Information
Revenues	211.5	178.0
Cost of sales	167.3	134.8
Selling, general, and administrative expenses:
Personnel expenses	18.8	17.5
Advertising expenses	0.3	0.4
Rent & related expenses	3.6	3.6
Other expenses	6.5	4.7
Depreciation	1.4	1.3
Floor plan interest expense	2.3	2.0
Other interest expense	4.5	0.1
Equity in earnings of affiliates	0.0	0.0
Segment income	6.8	13.6
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	33.0	32.3
Segment income	$ 33.0	$ 32.3