Segment Information - Revenues and Segment Income by Reportable Segment (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Segment Reporting Information
Revenues	$ 7,447.8	$ 7,339.0
Segment income	294.8	406.9
Retail automotive dealership
Segment Reporting Information
Revenues	6,478.0	6,299.8
Retail automotive dealership | Operating segments
Segment Reporting Information
Revenues	6,478.0	6,299.8
Segment income	198.4	256.7
Retail commercial truck dealership
Segment Reporting Information
Revenues	791.8	895.6
Retail commercial truck dealership | Operating segments
Segment Reporting Information
Revenues	791.8	895.6
Segment income	50.5	57.1
Other | Operating segments
Segment Reporting Information
Revenues	178.0	143.6
Segment income	13.6	12.1
Non-Automotive Investments | Operating segments
Segment Reporting Information
Revenues	0.0	0.0
Segment income	$ 32.3	$ 81.0