CONDENSED CONSOLIDATED STATEMENTS OF INCOME - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
REVENUE:
TOTAL REVENUE	$ 4,246.2	$ 3,742.5	$ 8,447.4	$ 7,324.8
COST OF SALES:
TOTAL COST OF SALES	3,515.5	3,029.4	6,966.7	5,915.5
GROSS PROFIT	730.7	713.1	1,480.7	1,409.3
OPERATING EXPENSES:
Selling, general, and administrative	476.5	408.6	945.1	811.6
Depreciation and amortization	18.2	16.8	36.9	33.5
Asset impairments	135.4	0.0	135.4	0.0
INCOME FROM OPERATIONS	100.5	287.7	363.3	564.2
OTHER EXPENSES (INCOME):
Floor plan interest expense	21.0	0.8	43.8	1.5
Other interest expense, net	45.1	39.3	89.2	76.6
Gain on dealership divestitures	(3.6)	(13.5)	(3.6)	(13.5)
Total other expenses, net	62.5	26.6	129.4	64.6
INCOME BEFORE INCOME TAXES	38.0	261.1	233.9	499.6
Income tax expense	9.9	64.8	58.7	121.9
NET INCOME	$ 28.1	$ 196.4	$ 175.2	$ 377.7
Basic—
Net income (in dollars per share)	$ 1.40	$ 9.37	$ 8.66	$ 17.78
Diluted—
Net income (in dollars per share)	$ 1.39	$ 9.34	$ 8.64	$ 17.70
WEIGHTED AVERAGE SHARES OUTSTANDING:
Basic (in shares)	20.1	20.9	20.2	21.2
Diluted (in shares)	20.2	21.0	20.3	21.3
New vehicle
REVENUE:
TOTAL REVENUE	$ 2,164.9	$ 1,942.7	$ 4,229.1	$ 3,710.4
COST OF SALES:
TOTAL COST OF SALES	2,009.8	1,757.7	3,911.2	3,346.5
Used vehicle
REVENUE:
TOTAL REVENUE	1,308.0	1,107.3	2,664.9	2,233.9
COST OF SALES:
TOTAL COST OF SALES	1,247.0	1,036.4	2,532.0	2,086.0
Parts and service
REVENUE:
TOTAL REVENUE	580.9	526.1	1,171.2	1,041.7
COST OF SALES:
TOTAL COST OF SALES	241.0	234.1	497.2	467.6
Finance and insurance, net
REVENUE:
TOTAL REVENUE	192.4	166.3	382.1	338.9
COST OF SALES:
TOTAL COST OF SALES	$ 17.7	$ 1.2	$ 26.3	$ 15.5
Restricted stock
WEIGHTED AVERAGE SHARES OUTSTANDING:
Incremental common shares (in shares)	0.1	0.0	0.0	0.0
Performance share units
WEIGHTED AVERAGE SHARES OUTSTANDING:
Incremental common shares (in shares)	0.0	0.1	0.1	0.1