Unaudited Condensed Consolidated Statements Of Cash Flows (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012
CASH PROVIDED BY (USED IN) OPERATING ACTIVITIES:
Net income	$ 172.9	$ 151.6
Adjustments to reconcile net income to net cash provided by operating activities:
Loss from discontinued operations	0.4	0.9
Depreciation and amortization	46.0	42.0
Amortization of debt issuance costs and accretion of debt discounts	2.8	2.8
Stock-based compensation expense	12.8	11.2
Deferred income tax provision	7.8	8.2
Franchise rights impairment	0	4.2
Net gain on asset sales and dispositions	(2.1)	(0.1)
Excess tax benefit from stock-based awards	(4.4)	(2.0)
Other	(4.2)	(0.2)
(Increase) decrease, net of effects from business combinations and divestitures:
Receivables	75.6	48.1
Inventory	(206.9)	(268.5)
Other assets	(11.2)	(23.4)
Increase (decrease), net of effects from business combinations and divestitures:
Vehicle floorplan payable-trade, net	152.1	120.3
Accounts payable	8.5	2.1
Other liabilities	23.0	22.8
Net cash provided by continuing operations	273.1	120.0
Net cash provided by (used in) discontinued operations	5.7	(0.5)
Net cash provided by operating activities	278.8	119.5
CASH PROVIDED BY (USED IN) INVESTING ACTIVITIES:
Proceeds from the sale of property and equipment	3.0	0.6
Proceeds from assets held for sale	1.8	10.7
Cash used in business acquisitions, net of cash acquired	(72.5)	0
Proceeds from the sale of restricted investments	0	0.4
Cash received from business divestitures, net of cash relinquished	10.1	0
Other	(2.4)	(1.7)
Net cash used in continuing operations	(130.9)	(74.8)
Net cash used in discontinued operations	0	0
Net cash used in investing activities	(130.9)	(74.8)
CASH PROVIDED BY (USED IN) FINANCING ACTIVITIES:
Repurchases of common stock	(18.5)	(531.9)
Proceeds from revolving credit facilities	375.0	715.0
Payment of revolving credit facilities	(515.0)	(680.0)
Proceeds from 5.5% Senior Notes due 2020	0	350.0
Payment of 7% Senior Notes due 2014	0	(14.7)
Payment of debt issuance costs	0	(6.0)
Net proceeds from vehicle floorplan payable - non-trade	28.9	102.9
Payments of mortgage facilities	(4.3)	(4.0)
Payments of capital leases and other debt obligations	(22.7)	(4.2)
Proceeds from the exercise of stock options	10.6	1.7
Excess tax benefit from stock-based awards	4.4	2.0
Net cash used in continuing operations	(141.6)	(69.2)
Net cash used in discontinued operations	(6.3)	0
Net cash used in financing activities	(147.9)	(69.2)
DECREASE IN CASH AND CASH EQUIVALENTS	0	(24.5)
CASH AND CASH EQUIVALENTS at beginning of period	69.7	86.6
CASH AND CASH EQUIVALENTS at end of period	69.7	62.1
Purchases of Property and Equipment [Member]
CASH PROVIDED BY (USED IN) INVESTING ACTIVITIES:
Purchases of property and equipment	(70.4)	(69.3)
Operating Lease Buyouts [Member]
CASH PROVIDED BY (USED IN) INVESTING ACTIVITIES:
Purchases of property and equipment	$ (0.5)	$ (15.5)