Consolidated Statements of Cash Flows (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
CASH PROVIDED BY (USED IN) OPERATING ACTIVITIES:
Net income	$ 374.9	$ 316.4	$ 281.4
Adjustments to reconcile net income to net cash provided by operating activities:
Loss from discontinued operations	0.9	0.9	2.8
Depreciation and amortization	95.3	87.3	83.7
Amortization of debt issuance costs and accretion of debt discounts	5.7	5.6	4.3
Stock-based compensation expense	21.3	18.6	18.4
Franchise rights impairment	0	4.2	0
Non-cash impairment charges	0.7	0.8	2.2
Write-off of deferred debt issuance costs	0	0	0.4
Net gain on asset sales and dispositions	(9.8)	(0.3)	(3.5)
Deferred income tax provision	9.9	26.8	31.1
Excess tax benefit from stock-based awards	(10.0)	(10.6)	(22.8)
Other	(6.8)	(4.0)	0.3
(Increase) decrease, net of effects from business combinations and divestitures:
Receivables	(46.3)	(112.0)	(127.4)
Inventory	(400.1)	(474.7)	70.1
Other assets	(21.5)	(35.8)	(23.6)
Increase (decrease), net of effects from business combinations and divestitures:
Vehicle floorplan payable-trade, net	364.2	404.0	(17.6)
Accounts payable	36.7	30.4	36.6
Other liabilities	63.8	60.0	39.5
Net cash provided by continuing operations	478.9	317.6	375.9
Net cash provided by (used in) discontinued operations	5.2	(1.0)	0.5
Net cash provided by operating activities	484.1	316.6	376.4
CASH PROVIDED BY (USED IN) INVESTING ACTIVITIES:
Proceeds from the sale of property and equipment	3.1	0.6	3.0
Proceeds from the disposal of assets held for sale	22.7	15.3	10.9
Insurance recoveries on property and equipment	2.5	1.0	0.1
Cash used in business acquisitions, net of cash acquired	(87.9)	(141.6)	(64.2)
Cash received from business divestitures, net of cash relinquished	10.1	6.8	4.9
Proceeds from the sale of restricted investments	0	0.4	0
Other	(5.6)	(2.9)	2.0
Net cash used in continuing operations	(257.8)	(297.8)	(206.2)
Net cash used in discontinued operations	0	0	0
Net cash used in investing activities	(257.8)	(297.8)	(206.2)
CASH PROVIDED BY (USED IN) FINANCING ACTIVITIES:
Repurchases of common stock	(67.3)	(575.6)	(579.8)
Proceeds from 5.5% Senior Notes due 2020	0	350.0	0
Proceeds from term loan facility	0	0	500.0
Payment of term loan facility	0	0	(533.4)
Payment of 7% Senior Notes due 2014	0	(14.7)	0
Proceeds from revolving credit facilities	815.0	1,280.0	940.0
Payment of revolving credit facilities	(1,055.0)	(1,235.0)	(625.0)
Payment of debt issuance costs	0	(6.0)	(13.0)
Net proceeds from vehicle floorplan payable - non-trade	89.0	138.1	40.1
Payments of mortgage facilities	(8.7)	(8.1)	(7.7)
Payments of capital lease and other debt obligations	(26.2)	(5.0)	(0.7)
Proceeds from the exercise of stock options	22.7	30.6	78.0
Excess tax benefit from stock-based awards	10.0	10.6	22.8
Net cash used in continuing operations	(220.5)	(35.1)	(178.7)
Net cash used in discontinued operations	(6.3)	(0.6)	0
Net cash used in financing activities	(226.8)	(35.7)	(178.7)
DECREASE IN CASH AND CASH EQUIVALENTS	(0.5)	(16.9)	(8.5)
CASH AND CASH EQUIVALENTS at beginning of period	69.7	86.6	95.1
CASH AND CASH EQUIVALENTS at end of period	69.2	69.7	86.6
Purchases of Property and Equipment [Member]
CASH PROVIDED BY (USED IN) INVESTING ACTIVITIES:
Purchases of property and equipment	(160.8)	(160.6)	(149.1)
Operating Lease Buyouts [Member]
CASH PROVIDED BY (USED IN) INVESTING ACTIVITIES:
Purchases of property and equipment	$ (41.9)	$ (16.8)	$ (13.8)