Segment Information - Revenues and Segment Income by Reportable Segment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Segment Reporting Information [Line Items]
Revenues	$ 30,455.2	$ 29,527.4	$ 27,814.8
Total cost of sales	25,441.9	24,593.6	22,976.0
Selling, general, and administrative expenses:
Personnel expenses	2,112.1	2,035.8	2,013.3
Advertising expenses	134.4	135.9	122.0
Rent & related expenses	418.2	389.3	370.7
Other expenses	873.8	839.6	717.7
Depreciation	158.0	141.0	127.3
Floor plan interest expense	189.8	133.1	52.4
Other interest expense	87.8	92.6	70.4
Equity in earnings of affiliates	200.7	293.7	494.2
Segment income	1,239.9	1,419.5	1,859.2
Goodwill impairment charges	0.0	40.7	0.0
Retail Automotive
Segment Reporting Information [Line Items]
Revenues	26,156.2	25,209.1	23,694.7
Total cost of sales	21,905.6	21,032.9	19,568.3
Selling, general, and administrative expenses:
Personnel expenses	1,775.6	1,709.9	1,709.1
Advertising expenses	129.4	130.8	116.7
Rent & related expenses	378.6	350.6	333.1
Other expenses	797.0	756.6	630.7
Depreciation	137.4	124.7	112.7
Floor plan interest expense	160.9	116.0	44.5
Other interest expense	82.1	90.3	65.1
Equity in earnings of affiliates	3.1	3.9	3.5
Segment income	792.7	860.5	1,118.0
Goodwill impairment charges		40.7
Retail Commercial Truck
Segment Reporting Information [Line Items]
Revenues	3,521.1	3,684.3	3,541.3
Total cost of sales	2,936.6	3,091.9	2,986.2
Selling, general, and administrative expenses:
Personnel expenses	264.3	253.6	234.0
Advertising expenses	3.2	3.3	3.5
Rent & related expenses	25.7	25.8	24.7
Other expenses	53.4	57.3	56.8
Depreciation	15.1	11.6	10.0
Floor plan interest expense	19.2	14.5	7.5
Other interest expense	0.0	1.3	3.9
Equity in earnings of affiliates	0.0	0.0	0.0
Segment income	203.6	225.0	214.7
Goodwill impairment charges		0.0
Other
Segment Reporting Information [Line Items]
Revenues	777.9	634.0	578.8
Total cost of sales	599.7	468.8	421.5
Selling, general, and administrative expenses:
Personnel expenses	72.2	72.3	70.2
Advertising expenses	1.8	1.8	1.8
Rent & related expenses	13.9	12.9	12.9
Other expenses	23.4	25.7	30.2
Depreciation	5.5	4.7	4.6
Floor plan interest expense	9.7	2.6	0.4
Other interest expense	5.7	1.0	1.4
Equity in earnings of affiliates	0.0	0.0	0.0
Segment income	46.0	44.2	35.8
Goodwill impairment charges		0.0
Non-Automotive Investments
Segment Reporting Information [Line Items]
Revenues	0.0	0.0	0.0
Total cost of sales	0.0	0.0	0.0
Selling, general, and administrative expenses:
Personnel expenses	0.0	0.0	0.0
Advertising expenses	0.0	0.0	0.0
Rent & related expenses	0.0	0.0	0.0
Other expenses	0.0	0.0	0.0
Depreciation	0.0	0.0	0.0
Floor plan interest expense	0.0	0.0	0.0
Other interest expense	0.0	0.0	0.0
Equity in earnings of affiliates	197.6	289.8	490.7
Segment income	$ 197.6	$ 289.8	$ 490.7