DESCRIPTION OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) $ in Millions		3 Months Ended					9 Months Ended
	Sep. 07, 2023 USD ($) newVehicleDealerships collisionCenter	Sep. 30, 2023 VehicleBrands dealership_location CollisionRepairCenters states franchise shares	Jun. 30, 2023 USD ($)	Mar. 31, 2023 USD ($)	Sep. 30, 2022 shares	Mar. 31, 2022 USD ($)	Sep. 30, 2023 USD ($) VehicleBrands dealership_location segment CollisionRepairCenters franchise states shares	Sep. 30, 2022 USD ($) shares	May 25, 2023 USD ($)
Business Organization [Line Items]
Number of franchises (in franchises) | franchise		181					181
Number of dealership locations (in dealership locations) | dealership_location		138					138
Number of vehicle brands (in vehicle brands) | VehicleBrands		31					31
Number of collision repair centers (in collision repair centers) | CollisionRepairCenters		31					31
Number of states (in states) | states		14					14
Number of reportable segments | segment							2
Transaction agreement, expected payments to acquire business	$ 1,200.0
Transaction agreement, dealerships to be acquired | newVehicleDealerships	20
Transaction agreement, collision centers to be acquired | collisionCenter	6
Retirement of common stock (in shares) | shares		0			0		1,070,126	1,069,203
Treasury stock, retired (in shares) | shares							1,124,330
Treasury stock, acquired value			$ 192.1	$ 20.7		$ 198.6
Cash paid to acquire treasury stock							$ 210.7	$ 200.0
Stock repurchase program, authorized amount									$ 250.0
Real Estate & Leasehold Improvements
Business Organization [Line Items]
Transaction agreement, expected payments to acquire business	$ 417.0
Restricted Share Units
Business Organization [Line Items]
Antidilutive securities excluded from computation of earnings per share | shares		466			403		2,235	1,937
Performance share units
Business Organization [Line Items]
Antidilutive securities excluded from computation of earnings per share | shares		3			0		0	394
Luxury Brands
Business Organization [Line Items]
Weighted brand mix (percent)							33.00%
Mid-line Import Brands
Business Organization [Line Items]
Weighted brand mix (percent)							39.00%
Domestic Brands
Business Organization [Line Items]
Weighted brand mix (percent)							28.00%