CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
CASH FLOW FROM OPERATING ACTIVITIES:
Net income	$ 147.1	$ 181.4
Adjustments to reconcile net income to net cash provided by operating activities—
Depreciation and amortization	18.7	16.7
Share-based compensation	10.5	8.6
Deferred income taxes	(0.1)	2.8
Unrealized gains on investments	(0.1)	(3.1)
Loaner vehicle amortization	11.8	6.7
Change in right-of-use assets	7.4	6.3
Other adjustments, net	5.1	0.8
Changes in operating assets and liabilities, net of acquisitions and divestitures—
Contracts-in-transit	57.7	64.5
Accounts receivable	(1.1)	5.2
Inventories	15.5	(33.3)
Other current assets	(75.4)	(109.5)
Floor plan notes payable—trade, net	10.4	(5.4)
Deferred revenue	10.5	(0.2)
Accounts payable and accrued liabilities	(31.0)	33.8
Operating lease liabilities	(6.8)	(5.9)
Other long-term assets and liabilities, net	(3.1)	2.3
Net cash provided by operating activities	177.1	171.7
CASH FLOW FROM INVESTING ACTIVITIES:
Capital expenditures—excluding real estate	(25.7)	(15.2)
Capital expenditures—real estate	(67.4)	0.0
Purchases of previously leased real estate	(11.9)	0.0
Proceeds from dealership divestitures	102.0	0.0
Purchases of debt securities—available-for-sale	(20.1)	(44.1)
Proceeds from the sale of debt securities—available-for-sale	9.5	3.5
Proceeds from the sale of equity securities	0.0	0.6
Net cash used in investing activities	(13.6)	(55.2)
CASH FLOW FROM FINANCING ACTIVITIES:
Floor plan borrowings—non-trade	2,532.8	1,799.6
Floor plan repayments—non-trade	(2,631.6)	(1,798.2)
Floor plan repayments—divestitures	(6.9)	0.0
Repayments of borrowings	(14.7)	(15.3)
Proceeds from revolving credit facility	582.8	0.0
Repayments of revolving credit facility	(582.8)	0.0
Purchases of treasury stock	50.0	30.2
Repurchases of common stock, associated with net share settlements of employee share-based awards	(9.8)	(10.9)
Net cash used in financing activities	(180.2)	(55.0)
Net (decrease) increase in cash and cash equivalents	(16.7)	61.5
CASH AND CASH EQUIVALENTS, beginning of period	45.7	235.3
CASH AND CASH EQUIVALENTS, end of period	$ 29.0	$ 296.8