Unaudited Condensed Consolidated Statements Of Cash Flows - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
CASH PROVIDED BY (USED IN) OPERATING ACTIVITIES:
Net income	$ 93.7	$ 98.1
Adjustments to reconcile net income to net cash provided by operating activities:
(Income) loss from discontinued operations	(0.4)	0.1
Depreciation and amortization	40.0	37.3
Amortization of debt issuance costs and accretion of debt discounts	1.7	1.4
Stock-based compensation expense	14.3	4.6
Deferred income tax provision	1.0	4.2
Net gain related to business/property dispositions	(12.2)	(9.6)
Non-cash impairment charges	1.3	0.0
Other	(0.1)	(7.3)
(Increase) decrease, net of effects from business combinations and divestitures:
Receivables	214.6	201.6
Inventory	(177.7)	(185.8)
Other assets	(74.2)	(16.0)
Increase (decrease), net of effects from business combinations and divestitures:
Vehicle floorplan payable - trade, net	63.6	(8.4)
Accounts payable	(0.5)	6.7
Other liabilities	33.6	58.9
Net cash provided by continuing operations	198.7	185.8
Net cash used in discontinued operations	0.0	(0.2)
Net cash provided by operating activities	198.7	185.6
CASH PROVIDED BY (USED IN) INVESTING ACTIVITIES:
Purchases of property and equipment	(101.5)	(90.1)
Property operating lease buy-outs	0.0	(3.3)
Proceeds from the sale of property and equipment	0.0	0.3
Proceeds from assets held for sale	1.8	13.4
Insurance recoveries on property and equipment	0.0	1.2
Cash received from business divestitures, net of cash relinquished	89.2	9.9
Cash used in business acquisitions, net of cash acquired	(1.9)	(5.8)
Other	(0.8)	(0.9)
Net cash used in continuing operations	(13.2)	(75.3)
Net cash used in discontinued operations	0.0	0.0
Net cash used in investing activities	(13.2)	(75.3)
CASH PROVIDED BY (USED IN) FINANCING ACTIVITIES:
Repurchases of common stock	(23.3)	0.0
Proceeds from revolving credit facility	0.0	260.0
Payments of revolving credit facility	0.0	(260.0)
Net payments of commercial paper	(60.0)	(177.0)
Net proceeds from (payments of) vehicle floorplan payable - non-trade	(124.2)	41.4
Payments of mortgage facility	0.0	(2.5)
Payments of capital leases and other debt obligations	(1.2)	(1.1)
Proceeds from the exercise of stock options	13.3	21.5
Payments of tax withholdings for stock-based awards	(2.3)	(0.4)
Net cash used in continuing operations	(197.7)	(118.1)
Net cash used in discontinued operations	0.0	0.0
Net cash used in financing activities	(197.7)	(118.1)
DECREASE IN CASH, CASH EQUIVALENTS, AND RESTRICTED CASH	(12.2)	(7.8)
CASH, CASH EQUIVALENTS, AND RESTRICTED CASH at beginning of period	71.1	65.4
CASH, CASH EQUIVALENTS, AND RESTRICTED CASH at end of period	$ 58.9	$ 57.6