GOODWILL AND INTANGIBLE FRANCHISE RIGHTS - Goodwill (Details) - USD ($) $ in Millions	12 Months Ended		216 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2019
Goodwill [Roll Forward]
Net, beginning balance	$ 1,783.4	$ 2,271.7
Reclassified from assets held for sale	0.9	118.5
Acquisitions - measurement period adjustments	(0.9)	(510.7)
Divestitures	(14.9)	(95.2)
Acquisitions	240.8
Reclassified to assets held for sale	(0.3)	(0.9)
Net, ending balance	2,009.0	1,783.4
Goodwill, impairment			$ 537.7
Dealerships
Goodwill [Roll Forward]
Net, beginning balance	1,246.8	1,561.4
Reclassified from assets held for sale	0.9	118.5
Acquisitions - measurement period adjustments	(0.9)	(337.0)
Divestitures	(14.9)	(95.2)
Acquisitions	240.8
Reclassified to assets held for sale	(0.3)	(0.9)
Net, ending balance	1,472.4	1,246.8
TCA
Goodwill [Roll Forward]
Net, beginning balance	536.6	710.3
Reclassified from assets held for sale	0.0	0.0
Acquisitions - measurement period adjustments	0.0	(173.7)
Divestitures	0.0	0.0
Acquisitions	0.0
Reclassified to assets held for sale	0.0	0.0
Net, ending balance	$ 536.6	$ 536.6