ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Increase (Decrease) in AOCI
Beginning balance	$ 3,136.0	$ 2,866.3	$ 2,974.3	$ 2,674.4
Other comprehensive income (loss) before reclassifications:
Pre-tax			47.0	41.8
Tax effect			1.9	(1.5)
Amount reclassified from accumulated other comprehensive income (loss):
Provision for income taxes			4.9	7.1
OTHER COMPREHENSIVE (LOSS) INCOME, NET OF TAX	(19.4)	18.8	33.3	17.7
Ending balance	3,053.1	2,976.2	3,053.1	2,976.2
Interest Rate Swaps
Amount reclassified from accumulated other comprehensive income (loss):
Pre-tax				(0.2)
Floorplan interest expense (pre-tax)
Amount reclassified from accumulated other comprehensive income (loss):
Pre-tax			(12.0)	(16.1)
Other interest expense, net (pre-tax)
Amount reclassified from accumulated other comprehensive income (loss):
Pre-tax			(8.4)	(13.3)
Accumulated Other Comprehensive Income (Loss)
Increase (Decrease) in AOCI
Beginning balance	54.4	27.0	1.6	28.1
Amount reclassified from accumulated other comprehensive income (loss):
OTHER COMPREHENSIVE (LOSS) INCOME, NET OF TAX	(19.4)	18.8	33.3	17.7
Ending balance	34.9	45.8	34.9	45.8
Accumulated Income (Loss) On Foreign Currency Translation
Increase (Decrease) in AOCI
Beginning balance			(56.5)	(37.4)
Other comprehensive income (loss) before reclassifications:
Pre-tax			54.8	35.4
Tax effect			0.0	0.0
Amount reclassified from accumulated other comprehensive income (loss):
Provision for income taxes			0.0	0.0
OTHER COMPREHENSIVE (LOSS) INCOME, NET OF TAX			54.8	35.4
Ending balance	(1.7)	(2.0)	(1.7)	(2.0)
Accumulated Income (Loss) On Foreign Currency Translation \| Interest Rate Swaps
Amount reclassified from accumulated other comprehensive income (loss):
Pre-tax				0.0
Accumulated Income (Loss) On Foreign Currency Translation \| Floorplan interest expense (pre-tax)
Amount reclassified from accumulated other comprehensive income (loss):
Pre-tax			0.0	0.0
Accumulated Income (Loss) On Foreign Currency Translation \| Other interest expense, net (pre-tax)
Amount reclassified from accumulated other comprehensive income (loss):
Pre-tax			0.0	0.0
Accumulated Income (Loss) On Interest Rate Swaps
Increase (Decrease) in AOCI
Beginning balance			58.2	65.6
Other comprehensive income (loss) before reclassifications:
Pre-tax			(7.8)	6.4
Tax effect			1.9	(1.5)
Amount reclassified from accumulated other comprehensive income (loss):
Provision for income taxes			4.9	7.1
OTHER COMPREHENSIVE (LOSS) INCOME, NET OF TAX			(21.5)	(17.7)
Ending balance	$ 36.7	$ 47.9	36.7	47.9
Accumulated Income (Loss) On Interest Rate Swaps \| Interest Rate Swaps
Amount reclassified from accumulated other comprehensive income (loss):
Pre-tax				(0.2)
Accumulated Income (Loss) On Interest Rate Swaps \| Floorplan interest expense (pre-tax)
Amount reclassified from accumulated other comprehensive income (loss):
Pre-tax			(12.0)	(16.1)
Accumulated Income (Loss) On Interest Rate Swaps \| Other interest expense, net (pre-tax)
Amount reclassified from accumulated other comprehensive income (loss):
Pre-tax			$ (8.4)	$ (13.3)

GROUP 1 AUTOMOTIVE INC 10-Q