Segment Information - Revenues and Segment Income by Reportable Segment (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Segment Reporting Information
Revenues	$ 7,696.7	$ 7,468.5	$ 15,144.5	$ 14,807.5
Segment income	325.5	400.3	620.3	807.2
Retail automotive dealership
Segment Reporting Information
Revenues	6,615.4	6,406.0	13,093.4	12,705.8
Retail automotive dealership | Operating segments
Segment Reporting Information
Revenues	6,615.4	6,406.0	13,093.4	12,705.8
Segment income	210.4	261.1	408.8	517.8
Retail commercial truck dealership
Segment Reporting Information
Revenues	892.3	919.2	1,684.1	1,814.8
Retail commercial truck dealership | Operating segments
Segment Reporting Information
Revenues	892.3	919.2	1,684.1	1,814.8
Segment income	51.7	55.5	102.2	112.6
Other | Operating segments
Segment Reporting Information
Revenues	189.0	143.3	367.0	286.9
Segment income	10.6	10.4	24.2	22.5
Non-Automotive Investments | Operating segments
Segment Reporting Information
Revenues	0.0	0.0	0.0	0.0
Segment income	$ 52.8	$ 73.3	$ 85.1	$ 154.3