DESCRIPTION OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details)			12 Months Ended
	Dec. 11, 2023 USD ($) collisionCenter	Dec. 17, 2021 USD ($) collisionCenter usedVehicleStore	Dec. 31, 2023 USD ($)	Dec. 31, 2023 USD ($)	Dec. 31, 2023 USD ($) shares	Dec. 31, 2023 USD ($) reportableSegment	Dec. 31, 2023 USD ($)	Dec. 31, 2023 USD ($) segment	Dec. 31, 2022 USD ($) shares	Dec. 31, 2021 USD ($) shares	May 25, 2023 USD ($)	Sep. 30, 2022	Nov. 19, 2021	Feb. 19, 2020
Accounting Policies [Line Items]
Restricted securities			$ 3,500,000	$ 3,500,000	$ 3,500,000	$ 3,500,000	$ 3,500,000	$ 3,500,000
Impairment of real estate				1,100,000					$ 0	$ 0
Advertising expense				47,500,000					50,100,000	30,700,000
Advertising credits and volume discounts				36,500,000					35,500,000	22,400,000
Investments			332,900,000	332,900,000	332,900,000	332,900,000	332,900,000	332,900,000
Total debt outstanding			3,230,100,000	3,230,100,000	3,230,100,000	$ 3,230,100,000	$ 3,230,100,000	$ 3,230,100,000	3,329,200,000
Revenues by major brand, disclosure percentage threshold							5.00%
Number of reportable segments						2		2
Goodwill			2,009,000,000	2,009,000,000	$ 2,009,000,000	$ 2,009,000,000	$ 2,009,000,000	$ 2,009,000,000	$ 1,783,400,000	$ 2,271,700,000
Purchase of treasury shares (in shares) | shares					1,316,167				1,635,030	0
Treasury stock, shares, retired (in shares) | shares					1,370,371				1,580,826	0
Stock repurchase program, authorized amount											$ 250,000,000
Remaining authorized repurchase amount			202,600,000	202,600,000	$ 202,600,000	202,600,000	202,600,000	202,600,000
Carrying Value of Collateralized Related Real Estate			3,230,000,000	3,230,000,000	3,230,000,000	3,230,000,000	3,230,000,000	3,230,000,000
Dealerships
Accounting Policies [Line Items]
Goodwill			1,472,400,000	1,472,400,000	1,472,400,000	1,472,400,000	1,472,400,000	1,472,400,000	$ 1,246,800,000	$ 1,561,400,000
LHM Acquisition
Accounting Policies [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
Goodwill		$ 1,205,300,000
Other long-term assets		5,600,000
Deferred revenue		667,600,000
Aggregate purchase price		$ 3,193,900,000
Acquired Finite-Lived Intangible Assets, Weighted Average Useful Life		5 years
LHM Acquisition | Insurance
Accounting Policies [Line Items]
Goodwill		$ 536,600,000
LHM Acquisition | Dealerships
Accounting Policies [Line Items]
Goodwill		$ 668,700,000
Jim Koons Dealerships
Accounting Policies [Line Items]
Number of new vehicle dealerships acquired (in new vehicle dealerships) | collisionCenter	20
Number of collision centers acquired (in collision centers) | collisionCenter	6
Goodwill	$ 231,700,000
Aggregate purchase price	1,500,000,000
Assets held for sale	103,800,000
New Floor Plan Facility | Jim Koons Dealerships
Accounting Policies [Line Items]
Aggregate purchase price	$ 256,100,000
Senior Notes
Accounting Policies [Line Items]
Carrying Value of Collateralized Related Real Estate			$ 2,227,700,000	$ 2,227,700,000	$ 2,227,700,000	$ 2,227,700,000	$ 2,227,700,000	$ 2,227,700,000	2,231,800,000
Senior Notes | 4.50% Senior Notes due 2028
Accounting Policies [Line Items]
Stated interest rate of debt instrument			4.50%	4.50%	4.50%	4.50%	4.50%	4.50%				4.50%		4.50%
Carrying Value of Collateralized Related Real Estate			$ 402,800,000	$ 402,800,000	$ 402,800,000	$ 402,800,000	$ 402,800,000	$ 402,800,000	409,500,000
Senior Notes | 4.75% Senior Notes due 2030
Accounting Policies [Line Items]
Stated interest rate of debt instrument			4.75%	4.75%	4.75%	4.75%	4.75%	4.75%				4.75%		4.75%
Carrying Value of Collateralized Related Real Estate			$ 442,200,000	$ 442,200,000	$ 442,200,000	$ 442,200,000	$ 442,200,000	$ 442,200,000	441,700,000
Senior Notes | 5.00% Senior Notes due 2032
Accounting Policies [Line Items]
Stated interest rate of debt instrument			5.00%	5.00%	5.00%	5.00%	5.00%	5.00%					5.00%
Carrying Value of Collateralized Related Real Estate			$ 592,300,000	$ 592,300,000	$ 592,300,000	$ 592,300,000	$ 592,300,000	$ 592,300,000	591,500,000
Senior Notes | 4.625% Senior Notes due 2029
Accounting Policies [Line Items]
Stated interest rate of debt instrument			4.625%	4.625%	4.625%	4.625%	4.625%	4.625%					4.625%
Carrying Value of Collateralized Related Real Estate			$ 790,400,000	$ 790,400,000	$ 790,400,000	$ 790,400,000	$ 790,400,000	$ 790,400,000	$ 789,100,000
Minimum
Accounting Policies [Line Items]
Loaner vehicle period of use before sale (in months)			6 months
Maximum
Accounting Policies [Line Items]
Loaner vehicle period of use before sale (in months)			12 months