Consolidated Statements of Cash Flows (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
CASH PROVIDED BY (USED IN) OPERATING ACTIVITIES:
Net income	$ 316.4	$ 281.4	$ 226.6
Adjustments to reconcile net income to net cash provided by operating activities:
Loss from discontinued operations	0.9	2.8	8.7
Depreciation and amortization	87.3	83.7	76.8
Amortization of debt issuance costs and accretion of debt discounts	5.6	4.3	3.5
Stock-based compensation expense	18.6	18.4	15.9
Franchise rights impairment	4.2	0	0
Non-cash impairment charges	0.8	2.2	3.7
Write-off of deferred debt issuance costs	0	0.4	3.5
Net gain on asset sales and dispositions	(0.3)	(3.5)	(2.8)
Deferred income tax provision	26.8	31.1	12.8
Excess tax benefit from stock-based awards	(10.6)	(22.8)	(7.7)
Other	(4.0)	0.3	2.3
(Increase) decrease, net of effects from business combinations and divestitures:
Receivables	(112.0)	(127.4)	(55.9)
Inventory	(474.7)	70.1	(448.6)
Other assets	(35.8)	(23.6)	28.6
Increase (decrease), net of effects from business combinations and divestitures:
Vehicle floorplan payable-trade, net	404.0	(17.6)	352.6
Accounts payable	35.1	38.4	11.8
Other liabilities	55.3	37.7	14.7
Net cash provided by continuing operations	317.6	375.9	246.5
Net cash provided by discontinued operations	(1.0)	0.5	5.3
Net cash provided by operating activities	316.6	376.4	251.8
CASH PROVIDED BY (USED IN) INVESTING ACTIVITIES:
Proceeds from the sale of property and equipment	0.6	3.0	5.4
Proceeds from the disposal of assets held for sale	15.3	10.9	12.4
Insurance recoveries on property and equipment	1.0	0.1	1.8
Cash used in business acquisitions, net of cash acquired	(141.6)	(64.2)	(73.1)
Cash received from business divestitures, net of cash relinquished	6.8	4.9	13.0
Proceeds from the sale of restricted investments	0.4	0	1.3
Other	(2.9)	2.0	1.0
Net cash provided by (used in) continuing operations	(297.8)	(206.2)	(200.0)
Net cash provided by (used in) discontinued operations	0	0	(0.2)
Net cash provided by (used in) investing activities	(297.8)	(206.2)	(200.2)
CASH PROVIDED BY (USED IN) FINANCING ACTIVITIES:
Repurchases of common stock	(575.6)	(579.8)	(524.4)
Proceeds from term loan facility	0	500.0	0
Payment of term loan facility	0	(533.4)	(66.6)
Proceeds from revolving credit facilities	1,280.0	940.0	305.0
Payment of revolving credit facilities	(1,235.0)	(625.0)	(125.0)
Payment of debt issuance costs	(6.0)	(13.0)	(11.9)
Net proceeds from (payments of) vehicle floorplan payable - non-trade	137.5	40.1	117.0
Payments of mortgage facilities	(8.1)	(7.7)	(7.3)
Payments of capital leases	(5.0)	(0.7)	(0.3)
Proceeds from the exercise of stock options	30.6	78.0	49.9
Excess tax benefit from stock-based awards	10.6	22.8	7.7
Net cash used in continuing operations	(35.7)	(178.7)	(125.9)
Net cash used in discontinued operations	0	0	(4.1)
Net cash used in financing activities	(35.7)	(178.7)	(130.0)
INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	(16.9)	(8.5)	(78.4)
CASH AND CASH EQUIVALENTS at beginning of period	86.6	95.1	173.5
CASH AND CASH EQUIVALENTS at end of period	69.7	86.6	95.1
5.5% Senior Notes Due 2020 [Member]
CASH PROVIDED BY (USED IN) FINANCING ACTIVITIES:
Proceeds from Senior Unsecured Notes	350.0	0	0
6.75% Senior Notes Due 2018 [Member]
CASH PROVIDED BY (USED IN) FINANCING ACTIVITIES:
Proceeds from Senior Unsecured Notes	0	0	394.0
7% Senior Notes Due 2014 [Member] | Unsecured Debt [Member]
CASH PROVIDED BY (USED IN) FINANCING ACTIVITIES:
Payment of 7% Senior Notes due 2014	(14.7)	0	(117.9)
Floating Rate Senior Notes Due 2013 [Member] | Unsecured Debt [Member]
CASH PROVIDED BY (USED IN) FINANCING ACTIVITIES:
Payment of Senior Unsecured Notes	0	0	(146.1)
Purchases of Property and Equipment [Member]
CASH PROVIDED BY (USED IN) INVESTING ACTIVITIES:
Purchases of property and equipment	(160.6)	(149.1)	(150.4)
Operating Lease Buyouts [Member]
CASH PROVIDED BY (USED IN) INVESTING ACTIVITIES:
Purchases of property and equipment	$ (16.8)	$ (13.8)	$ (11.4)