Unaudited Condensed Consolidated Statements Of Cash Flows (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011
CASH PROVIDED BY (USED IN) OPERATING ACTIVITIES:
Net income	$ 233.2	$ 212.0
Adjustments to reconcile net income to net cash provided by operating activities:
Loss from discontinued operations	1.2	2.3
Amortization of debt issuance costs and discounts	4.2	3.2
Depreciation and Amortization	64.9	62.7
Stock-based compensation expense	15.2	15.7
Deferred income tax provision	15.4	15.9
Non-cash impairment charges	0.3	0
Franchise rights impairment	4.2	0
Net gain on asset sales and dispositions	(0.2)	(3.0)
Other	(2.6)	(0.2)
(Increase) decrease, net of effects from business combinations and divestitures:
Receivables	71.7	57.5
Inventory	(332.9)	277.6
Other assets	(25.2)	(10.5)
Increase (decrease), net of effects from business combinations and divestitures:
Vehicle floorplan payable-trade, net	197.1	(336.7)
Accounts payable	17.1	5.0
Other liabilities	48.8	9.3
Net cash provided by continuing operations	312.4	310.8
Net cash provided by (used in) discontinued operations	(0.7)	0.3
Net cash provided by operating activities	311.7	311.1
CASH PROVIDED BY (USED IN) INVESTING ACTIVITIES:
Proceeds from the sale of property and equipment	0.6	3.0
Proceeds from assets held for sale	11.8	9.0
Insurance recoveries on property and equipment	1.0	0
Cash used in business acquisitions, net of cash acquired	0	(64.2)
Proceeds from the sale of restricted investments	0.4	0
Cash received from business divestitures, net of cash relinquished	0	4.9
Other	(3.0)	0.2
Net cash used in continuing operations	(113.8)	(174.7)
Net cash used in discontinued operations	0	0
Net cash used in investing activities	(113.8)	(174.7)
CASH PROVIDED BY (USED IN) FINANCING ACTIVITIES:
Repurchases of common stock	(538.3)	(335.0)
Proceeds from revolving credit facilities	820.0	300.0
Payment of revolving credit facilities	(920.0)	(180.0)
Proceeds from 5.5% Senior Notes due 2020	350.0	0
Payment of 7% Senior Notes due 2014	(14.7)	0
Payment of debt issuance costs	(6.0)	0
Net proceeds from (payments of) vehicle floorplan payable - non-trade	104.9	(28.3)
Payments of mortgage facilities	(6.0)	(5.7)
Payments of capital leases	(4.5)	(0.5)
Proceeds from the exercise of stock options	20.7	66.3
Excess tax benefit from stock-based awards	8.0	19.0
Net cash used in continuing operations	(185.9)	(164.2)
Net cash used in discontinued operations	0	0
Net cash used in financing activities	(185.9)	(164.2)
INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	12.0	(27.8)
CASH AND CASH EQUIVALENTS at beginning of period	86.6	95.1
CASH AND CASH EQUIVALENTS at end of period	98.6	67.3
Purchases of Property and Equipment [Member]
CASH PROVIDED BY (USED IN) INVESTING ACTIVITIES:
Purchases of property and equipment	(107.8)	(113.8)
Operating Lease Buyouts [Member]
CASH PROVIDED BY (USED IN) INVESTING ACTIVITIES:
Purchases of property and equipment	$ (16.8)	$ (13.8)