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Segment Information (Details) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
Segment Information (Details) $ in Millions	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Sep. 30, 2023 USD ($) segment	Sep. 30, 2022 USD ($)	Dec. 31, 2022 USD ($)
Segment Reporting Information
Number of reportable segments \| segment			4
Revenues and segment income by reportable segment
Revenues	$ 7,447.8	$ 6,920.7	$ 22,255.3	$ 20,803.0
Segment income	356.5	467.2	1,163.7	1,464.4
Intersegment Elimination
Revenues and segment income by reportable segment
Revenues	0.0	0.0	0.0	0.0
Segment income	0.0	0.0	$ 0.0	0.0
Retail automotive dealership
Segment Reporting Information
Number of reportable segments \| segment			1
Number of operating segments \| segment			6
Revenues and segment income by reportable segment
Revenues	6,325.4	5,757.8	$ 19,031.2	17,784.3	$ 23,700.0
Retail automotive dealership \| Operating segments
Revenues and segment income by reportable segment
Revenues	6,325.4	5,757.8	19,031.2	17,784.3
Segment income	200.8	269.2	718.6	880.9
Retail commercial truck dealership
Revenues and segment income by reportable segment
Revenues	964.7	1,019.5	2,779.5	2,580.5
Retail commercial truck dealership \| Operating segments
Revenues and segment income by reportable segment
Revenues	964.7	1,019.5	2,779.5	2,580.5
Segment income	61.1	52.8	173.7	163.6
Other \| Operating segments
Revenues and segment income by reportable segment
Revenues	157.7	143.4	444.6	438.2
Segment income	10.4	9.6	32.9	28.9
Non-Automotive Investments \| Operating segments
Revenues and segment income by reportable segment
Revenues	0.0	0.0	0.0	0.0
Segment income	$ 84.2	$ 135.6	$ 238.5	$ 391.0