Segment Information - Total Assets, Equity Method Investments, and Capital Expenditures by Reportable Segment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Segment Reporting Information [Line Items]
Total assets	$ 15,671.5	$ 14,114.6
Equity method investments	1,774.9	1,636.9
Capital expenditures	375.3	282.5	$ 248.9
Operating segments | Retail automotive dealership
Segment Reporting Information [Line Items]
Total assets	11,408.3	10,483.3
Equity method investments	44.5	41.1
Capital expenditures	306.9	245.6	239.4
Operating segments | Retail commercial truck dealership
Segment Reporting Information [Line Items]
Total assets	1,690.8	1,471.9
Equity method investments	0.0	0.0
Capital expenditures	60.1	31.2	6.3
Operating segments | Other
Segment Reporting Information [Line Items]
Total assets	842.0	563.6
Equity method investments	0.0	0.0
Capital expenditures	8.3	5.7	3.2
Operating segments | Non-Automotive Investments
Segment Reporting Information [Line Items]
Total assets	1,730.4	1,595.8
Equity method investments	1,730.4	1,595.8
Capital expenditures	$ 0.0	$ 0.0	$ 0.0