GOODWILL AND INTANGIBLE FRANCHISE RIGHTS - Narrative (Details)			1 Months Ended	12 Months Ended
	Dec. 11, 2023 USD ($) collisionCenter	Dec. 17, 2021 USD ($) collisionCenter usedVehicleStore	Dec. 31, 2023 USD ($)	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Business Acquisition [Line Items]
Goodwill acquired				$ 240,800,000
Goodwill			$ 2,009,000,000	2,009,000,000	$ 1,783,400,000	$ 2,271,700,000
Asset impairment charges			44,100,000
Dealerships
Business Acquisition [Line Items]
Goodwill acquired				240,800,000
Goodwill			$ 1,472,400,000	1,472,400,000	1,246,800,000	$ 1,561,400,000
Franchise rights
Business Acquisition [Line Items]
Intangible assets acquired					517,700,000
Goodwill and intangible asset impairment				117,200,000	$ 0
Non-cash, impairment of intangible assets, finite-lived, pre-tax				$ 73,100,000
LHM Acquisition
Business Acquisition [Line Items]
Number of new vehicle dealerships acquired (in new vehicle dealerships) | collisionCenter		54
Number of used cars stores acquired (in used cars stores) | usedVehicleStore		7
Number of collision centers acquired (in collision centers) | collisionCenter		11
Aggregate purchase price		$ 3,193,900,000
Goodwill		1,205,300,000
Intangible franchise rights		1,309,700,000
Other long-term assets		5,600,000
LHM Acquisition | Insurance
Business Acquisition [Line Items]
Goodwill		536,600,000
LHM Acquisition | Dealerships
Business Acquisition [Line Items]
Goodwill		$ 668,700,000
Jim Koons Dealerships
Business Acquisition [Line Items]
Number of new vehicle dealerships acquired (in new vehicle dealerships) | collisionCenter	20
Number of collision centers acquired (in collision centers) | collisionCenter	6
Aggregate purchase price	$ 1,500,000,000
Goodwill	231,700,000
Intangible franchise rights	429,000,000.0
Jim Koons Dealerships | Franchise rights
Business Acquisition [Line Items]
Intangible franchise rights	$ 429,000,000.0