INVENTORIES AND FLOOR PLAN NOTES PAYABLE - Schedule of Inventories (Details) - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023
Inventory [Line Items]
Total inventories	$ 6,242.9	$ 4,753.9
New vehicles
Inventory [Line Items]
Total inventories	3,892.0	2,886.3
Used vehicles
Inventory [Line Items]
Total inventories	2,060.0	1,637.5
Parts and accessories
Inventory [Line Items]
Total inventories	$ 290.9	$ 230.1

Amount after valuation and LIFO reserves of inventory expected to be sold, or consumed within one year or operating cycle, if longer.

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 852
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
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Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
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-Publisher FASB
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(6))
-Publisher FASB
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