Consolidated Statements of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022		Dec. 31, 2021
CASH PROVIDED BY (USED IN) OPERATING ACTIVITIES:
Net income	$ 1,021.1	$ 1,377.4		$ 1,373.0
Adjustments to reconcile net income to net cash provided by operating activities:
Loss (income) from discontinued operations	(0.9)	0.3		0.3
Depreciation and amortization	220.5	200.3		193.3
Amortization of debt issuance costs and accretion of debt discounts	9.6	7.2		4.9
Stock-based compensation expense	39.7	31.5		35.0
Provision for credit losses on auto loans receivable	45.9	43.8	[1]	0.0
Deferred income tax provision (benefit)	20.1	1.3		(17.4)
Net gain related to business/property dispositions	(9.1)	(16.3)		(18.1)
Gain on equity investments	(5.2)	(2.9)		(10.9)
Loss (gain) on corporate-owned life insurance asset	(16.4)	19.4		(12.7)
Gain on sale of auto loans receivable	(8.1)	0.0		0.0
Other	6.4	1.6		2.6
(Increase) decrease, net of effects from business acquisitions and divestitures:
Receivables	(178.2)	(129.2)		114.9
Auto loans receivable, net	(229.9)	0.0		0.0
Inventory	(950.1)	(175.5)		800.4
Other assets	(84.2)	(58.4)		92.2
Increase (decrease), net of effects from business acquisitions and divestitures:
Vehicle floorplan payable-trade	813.4	461.1		(1,059.7)
Accounts payable	8.1	(68.9)		57.2
Other liabilities	21.6	(24.3)		73.0
Net cash provided by continuing operations	724.3	1,668.4		1,628.0
Net cash used in discontinued operations	(0.3)	(0.3)		(0.3)
Net cash provided by operating activities	724.0	1,668.1		1,627.7
CASH PROVIDED BY (USED IN) INVESTING ACTIVITIES:
Purchases of property and equipment	(410.3)	(329.0)		(215.7)
Proceeds from the disposal of assets held for sale	7.9	22.8		37.1
Cash used in business acquisitions, net of cash acquired	(271.4)	(191.6)		(432.7)
Cash received from business divestitures, net of cash relinquished	23.2	55.2		48.7
Originations of auto loans receivable acquired through third-party dealers	(110.9)	(56.0)		0.0
Collections on auto loans receivable acquired through third-party dealers	135.0	36.4		0.0
Proceeds from the sale of auto loans receivable	68.7	0.0		0.0
Proceeds from the sale of equity securities	1.4	1.8		109.4
Investment in equity securities	0.0	(12.0)		(5.5)
Other	(13.5)	(6.9)		(1.6)
Net cash used in continuing operations	(569.9)	(479.3)		(460.3)
Net cash used in discontinued operations	0.0	0.0		0.0
Net cash used in investing activities	(569.9)	(479.3)		(460.3)
CASH PROVIDED BY (USED IN) FINANCING ACTIVITIES:
Repurchases of common stock	(874.4)	(1,699.5)		(2,318.2)
Net proceeds from (payments of) commercial paper	390.0	(290.0)		340.0
Proceeds from non-recourse debt	324.0	40.7		0.0
Payments of non-recourse debt	(392.7)	(35.6)		0.0
Payment of debt issuance costs	(6.6)	(7.1)		(8.0)
Net proceeds from (payments of) vehicle floorplan payable - non-trade	425.3	178.6		(263.9)
Payment of other debt obligations	(12.6)	(12.0)		(10.9)
Proceeds from the exercise of stock options	1.9	3.4		54.5
Payments of tax withholdings for stock-based awards	(27.4)	(31.3)		(18.0)
Net cash used in continuing operations	(172.5)	(1,154.0)		(1,676.5)
Net cash used in discontinued operations	0.0	0.0		0.0
Net cash used in financing activities	(172.5)	(1,154.0)		(1,676.5)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect	(18.4)	34.8		(509.1)
CASH, CASH EQUIVALENTS, AND RESTRICTED CASH at beginning of year	95.4	60.6		569.7
CASH, CASH EQUIVALENTS, AND RESTRICTED CASH at end of year	77.0	95.4		60.6
Senior Notes at Three Point Eight Five Percent Due 2032 [Member]
CASH PROVIDED BY (USED IN) FINANCING ACTIVITIES:
Proceeds from Senior Notes	0.0	698.8		0.0
Senior Notes at One Point Nine Five Percent Due 2028 [Member]
CASH PROVIDED BY (USED IN) FINANCING ACTIVITIES:
Proceeds from Senior Notes	0.0	0.0		399.2
Senior Notes at Two Point Four Percent Due 2031 [Member]
CASH PROVIDED BY (USED IN) FINANCING ACTIVITIES:
Proceeds from Senior Notes	0.0	0.0		448.8
Senior Notes at Three Point Three Five Percent Due 2021
CASH PROVIDED BY (USED IN) FINANCING ACTIVITIES:
Payment of Senior Notes	$ 0.0	$ 0.0		$ (300.0)

[1] (1) Reflects activity that occurred after the acquisition of CIG Financial on October 1, 2022. Provision for credit losses includes initial credit loss expense of $34.2 million associated with the auto loan portfolio acquired as part of the acquisition.