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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, 2022 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2022 USD ($) segment	Sep. 30, 2021 USD ($)	Dec. 31, 2021 USD ($)
Segment Reporting Information
Number of reportable segments \| segment			4
Revenues and segment income by reportable segment
Revenues	$ 6,920.7	$ 6,497.3	$ 20,803.0	$ 19,258.6
Segment income	467.2	476.1	1,464.4	1,187.4
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	5,757.8	5,634.9	$ 17,784.3	17,039.4	$ 22,500.0
Retail automotive dealership \| Operating segments
Revenues and segment income by reportable segment
Revenues	5,757.8	5,634.9	17,784.3	17,039.4
Segment income	269.2	299.6	880.9	772.9
Retail commercial truck dealership
Revenues and segment income by reportable segment
Revenues	1,019.5	717.3	2,580.5	1,777.3
Retail commercial truck dealership \| Operating segments
Revenues and segment income by reportable segment
Revenues	1,019.5	717.3	2,580.5	1,777.3
Segment income	52.8	48.3	163.6	115.5
Other \| Operating segments
Revenues and segment income by reportable segment
Revenues	143.4	145.1	438.2	441.9
Segment income	9.6	9.8	28.9	24.2
Non-Automotive Investments \| Operating segments
Revenues and segment income by reportable segment
Revenues	0.0	0.0	0.0	0.0
Segment income	$ 135.6	$ 118.4	$ 391.0	$ 274.8