Unaudited Condensed Consolidated Statements Of Cash Flows - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
CASH PROVIDED BY (USED IN) OPERATING ACTIVITIES:
Net income	$ 985.9	$ 230.1
Adjustments to reconcile net income to net cash provided by operating activities:
Loss from discontinued operations	0.2	0.2
Depreciation and amortization	143.4	149.0
Amortization of debt issuance costs and accretion of debt discounts	3.5	3.5
Stock-based compensation expense	31.6	22.9
Deferred income tax benefit	(15.1)	(25.0)
Net gain related to business/property dispositions	(6.3)	(2.4)
Goodwill impairment	0.0	318.3
Franchise rights impairment	0.0	57.5
Non-cash impairment charges	3.2	11.4
Gain on equity investments	(10.9)	(212.7)
Other	(8.2)	(4.0)
(Increase) decrease, net of effects from business acquisitions and divestitures:
Receivables	215.6	232.7
Inventory	1,131.3	827.4
Other assets	70.9	81.6
Increase (decrease), net of effects from business acquisitions and divestitures:
Vehicle floorplan payable - trade	(1,083.5)	(661.8)
Accounts payable	19.1	57.5
Other liabilities	78.7	78.1
Net cash provided by continuing operations	1,559.4	1,164.3
Net cash used in discontinued operations	(0.2)	0.0
Net cash provided by operating activities	1,559.2	1,164.3
CASH PROVIDED BY (USED IN) INVESTING ACTIVITIES:
Purchases of property and equipment	(161.3)	(113.1)
Proceeds from assets held for sale	34.8	8.2
Insurance recoveries on property and equipment	1.6	1.9
Cash received from business divestitures, net of cash relinquished	4.8	2.2
Cash used in business acquisitions, net of cash acquired	(209.1)	(0.4)
Proceeds from sale of equity securities	109.4	0.0
Investment in equity securities	(3.3)	(50.0)
Other	(2.4)	(0.4)
Net cash used in continuing operations	(225.5)	(151.6)
Net cash used in discontinued operations	0.0	0.0
Net cash used in investing activities	(225.5)	(151.6)
CASH PROVIDED BY (USED IN) FINANCING ACTIVITIES:
Repurchases of common stock	(1,936.5)	(80.0)
Proceeds from revolving credit facility	0.0	1,110.0
Payments of revolving credit facility	0.0	(1,110.0)
Net payments of commercial paper	0.0	(170.0)
Payment of debt issuance costs	(8.0)	(11.0)
Net payments of vehicle floorplan payable - non-trade	(452.0)	(609.7)
Payments of other debt obligations	(7.5)	(4.6)
Proceeds from the exercise of stock options	42.6	31.5
Payments of tax withholdings for stock-based awards	(17.9)	(8.2)
Net cash used in continuing operations	(1,831.3)	(704.6)
Net cash used in discontinued operations	0.0	0.0
Net cash used in financing activities	(1,831.3)	(704.6)
INCREASE (DECREASE) IN CASH, CASH EQUIVALENTS, AND RESTRICTED CASH	(497.6)	308.1
CASH, CASH EQUIVALENTS, AND RESTRICTED CASH at beginning of period	569.7	42.5
CASH, CASH EQUIVALENTS, AND RESTRICTED CASH at end of period	72.1	350.6
1.95% Senior Notes Due 2028
CASH PROVIDED BY (USED IN) FINANCING ACTIVITIES:
Proceeds from senior notes	399.2	0.0
2.4% Senior Notes Due 2031
CASH PROVIDED BY (USED IN) FINANCING ACTIVITIES:
Proceeds from senior notes	448.8	0.0
4.75% Senior Notes Due 2030 [Member]
CASH PROVIDED BY (USED IN) FINANCING ACTIVITIES:
Proceeds from senior notes	0.0	497.4
3.35% Senior Notes Due 2021 [Member]
CASH PROVIDED BY (USED IN) FINANCING ACTIVITIES:
Payment of senior notes	(300.0)	0.0
5.5% Senior Notes Due 2020 [Member]
CASH PROVIDED BY (USED IN) FINANCING ACTIVITIES:
Payment of senior notes	$ 0.0	$ (350.0)