INVENTORIES AND FLOOR PLAN NOTES PAYABLE - Schedule of Inventories (Details) - USD ($) $ in Millions	Jun. 30, 2026	Dec. 31, 2025
Inventory [Line Items]
Total inventories	$ 6,516.8	$ 6,119.6
New vehicle
Inventory [Line Items]
Total inventories	3,731.0	3,586.1
Used vehicles
Inventory [Line Items]
Total inventories	2,523.8	2,266.7
Parts and accessories
Inventory [Line Items]
Total inventories	$ 262.0	$ 266.8

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/disclosureRef
-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
-Section S50
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480657/210-10-S50-3

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Topic 852
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 10
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481372/852-10-55-10

Reference 3: http://www.xbrl.org/2003/role/exampleRef
-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483467/210-10-45-1

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
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-Publisher FASB
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