Unaudited Condensed Consolidated Statements Of Cash Flows - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021
CASH PROVIDED BY (USED IN) OPERATING ACTIVITIES:
Net income	$ 1,091.0	$ 985.9
Adjustments to reconcile net income to net cash provided by operating activities:
Loss from discontinued operations	0.3	0.2
Depreciation and amortization	148.9	143.4
Amortization of debt issuance costs and accretion of debt discounts	4.5	3.5
Stock-based compensation expense	26.3	31.6
Deferred income tax provision (benefit)	5.5	(15.1)
Net gain related to business/property dispositions	(17.1)	(6.3)
Non-cash impairment charges	1.0	3.2
Loss (gain) on equity investments	0.1	(10.9)
Loss (gain) on corporate-owned life insurance asset	26.0	(8.0)
Other	0.0	(0.2)
(Increase) decrease, net of effects from business acquisitions and divestitures:
Receivables	80.3	215.6
Inventory	(9.1)	1,131.3
Other assets	(28.6)	70.9
Increase (decrease), net of effects from business acquisitions and divestitures:
Vehicle floorplan payable - trade	124.0	(1,083.5)
Accounts payable	(52.2)	19.1
Other liabilities	42.7	78.7
Net cash provided by continuing operations	1,443.6	1,559.4
Net cash used in discontinued operations	(0.3)	(0.2)
Net cash provided by operating activities	1,443.3	1,559.2
CASH PROVIDED BY (USED IN) INVESTING ACTIVITIES:
Purchases of property and equipment	(236.2)	(161.3)
Proceeds from assets held for sale	22.8	34.8
Insurance recoveries on property and equipment	0.3	1.6
Cash received from business divestitures, net of cash relinquished	55.2	4.8
Cash used in business acquisitions, net of cash acquired	0.0	(209.1)
Proceeds from the sale of equity securities	0.0	109.4
Investment in equity securities	0.0	(3.3)
Deposits for investment	(81.6)	0.0
Other	(7.8)	(2.4)
Net cash used in continuing operations	(247.3)	(225.5)
Net cash used in discontinued operations	0.0	0.0
Net cash used in investing activities	(247.3)	(225.5)
CASH PROVIDED BY (USED IN) FINANCING ACTIVITIES:
Repurchases of common stock	(1,177.4)	(1,936.5)
Net payments of commercial paper	(340.0)	0.0
Payment of debt issuance costs	(6.6)	(8.0)
Net proceeds from (payments of) vehicle floorplan payable - non-trade	46.4	(452.0)
Payments of other debt obligations	(8.7)	(7.5)
Proceeds from the exercise of stock options	3.4	42.6
Payments of tax withholdings for stock-based awards	(29.5)	(17.9)
Net cash used in continuing operations	(813.6)	(1,831.3)
Net cash used in discontinued operations	0.0	0.0
Net cash used in financing activities	(813.6)	(1,831.3)
INCREASE (DECREASE) IN CASH, CASH EQUIVALENTS, AND RESTRICTED CASH	382.4	(497.6)
CASH, CASH EQUIVALENTS, AND RESTRICTED CASH at beginning of period	60.6	569.7
CASH, CASH EQUIVALENTS, AND RESTRICTED CASH at end of period	443.0	72.1
1.95% Senior Notes Due 2028
CASH PROVIDED BY (USED IN) FINANCING ACTIVITIES:
Proceeds from Senior Notes	0.0	399.2
2.4% Senior Notes Due 2031
CASH PROVIDED BY (USED IN) FINANCING ACTIVITIES:
Proceeds from Senior Notes	0.0	448.8
3.85% Senior Notes Due 2032
CASH PROVIDED BY (USED IN) FINANCING ACTIVITIES:
Proceeds from Senior Notes	698.8	0.0
3.35% Senior Notes Due 2021
CASH PROVIDED BY (USED IN) FINANCING ACTIVITIES:
Payment of Senior Notes	$ 0.0	$ (300.0)