ACQUISITIONS AND DIVESTITURES - Schedule of Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Millions			12 Months Ended
	Dec. 11, 2023	Dec. 17, 2021	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Assets
Goodwill			$ 2,009.0	$ 1,783.4	$ 2,271.7
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities [Abstract]
Total liabilities assumed			6.4	$ 21.3
Jim Koons Dealerships
Assets
Payments to acquire businesses, gross	$ 936.8
Inventories, net	311.6
Other current assets	10.3
Assets held for sale	103.8
Total current assets	425.7
Property and equipment, net	420.0
Goodwill	231.7
Intangible franchise rights	429.0
Operating lease right-of-use assets	11.2
Total assets acquired	1,517.6
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities [Abstract]
Operating lease liabilities	11.2
Other long-term liabilities	6.4
Total liabilities assumed	17.6
Net assets acquired	$ 1,500.0
LHM Acquisition
Assets
Payments to acquire businesses, gross		$ 3,480.0
Common stock offering		666.9
Payable to sellers		6.0
Cash and cash equivalents		287.4
Investments		133.5
Contracts-in-transit, net		99.5
Accounts receivable, net		110.0
Inventories, net		282.1
Other current assets		25.0
Total current assets		937.5
Property and equipment, net		805.6
Goodwill		1,205.3
Intangible franchise rights		1,309.7
Operating lease right-of-use assets		34.1
Deferred income taxes		139.7
Other long-term assets		5.6
Total assets acquired		4,437.6
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities [Abstract]
Accounts payable and accrued liabilities		229.5
Operating lease liabilities		34.1
Deferred revenue		667.6
Other long-term liabilities		25.2
Total liabilities assumed		956.4
Net assets acquired		$ 3,481.2
Series of Individually Immaterial Business Acquisitions
Assets
Payments to acquire businesses, gross			455.1
Purchase price holdbacks			21.0
Payable to sellers			9.6
Real estate			99.9
Inventories, net			37.5
Other			(3.5)
Loaner vehicles			8.9
Property and equipment, net			4.2
Goodwill			110.5
Intangible franchise rights			228.2
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities [Abstract]
Net assets acquired			$ 485.7