Segment Information - Revenues and Segment Income by Reportable Segment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Segment Reporting Information [Line Items]
Revenues	$ 29,527.4	$ 27,814.8	$ 25,554.7
Gross profit	4,933.8	4,838.8	4,440.8
Selling, general and administrative expenses	3,400.6	3,223.7	2,962.9
Floor plan interest expense	133.1	52.4	26.2
Other interest expense	92.6	70.4	68.6
Depreciation	141.0	127.3	121.5
Equity in earnings of affiliates	293.7	494.2	374.5
Income from continuing operations before income taxes	1,419.5	1,859.2	1,607.7
Impairment charges	40.7	0.0	0.0
Retail automotive dealership
Segment Reporting Information [Line Items]
Revenues	25,209.1	23,694.7	22,513.3
Impairment charges	40.7
Retail commercial truck dealership
Segment Reporting Information [Line Items]
Revenues	3,684.3	3,541.3	2,465.7
Impairment charges	0.0
Other
Segment Reporting Information [Line Items]
Impairment charges	0.0
Operating segments | Retail automotive dealership
Segment Reporting Information [Line Items]
Revenues	25,209.1	23,694.7	22,513.3
Gross profit	4,176.2	4,126.4	3,870.2
Selling, general and administrative expenses	2,948.8	2,790.4	2,607.3
Floor plan interest expense	116.0	44.5	23.9
Other interest expense	90.3	65.1	63.8
Depreciation	124.7	112.7	108.7
Equity in earnings of affiliates	3.9	3.5	8.2
Income from continuing operations before income taxes	860.5	1,118.0	1,046.6
Operating segments | Retail commercial truck dealership
Segment Reporting Information [Line Items]
Revenues	3,684.3	3,541.3	2,465.7
Gross profit	592.4	555.1	416.9
Selling, general and administrative expenses	339.2	318.3	243.3
Floor plan interest expense	14.5	7.5	1.9
Other interest expense	1.3	3.9	3.3
Depreciation	11.6	10.0	7.9
Equity in earnings of affiliates	0.0	0.0	0.0
Income from continuing operations before income taxes	225.0	214.7	160.3
Operating segments | Other
Segment Reporting Information [Line Items]
Revenues	634.0	578.8	575.7
Gross profit	165.2	157.3	153.7
Selling, general and administrative expenses	112.6	115.0	112.3
Floor plan interest expense	2.6	0.4	0.4
Other interest expense	1.0	1.4	1.5
Depreciation	4.7	4.6	4.9
Equity in earnings of affiliates	0.0	0.0	0.0
Income from continuing operations before income taxes	44.2	35.8	34.5
Operating segments | Non-Automotive Investments
Segment Reporting Information [Line Items]
Revenues	0.0	0.0	0.0
Gross profit	0.0	0.0	0.0
Selling, general and administrative expenses	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
Depreciation	0.0	0.0	0.0
Equity in earnings of affiliates	289.8	490.7	366.3
Income from continuing operations before income taxes	$ 289.8	$ 490.7	$ 366.3