Segment Information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2011		Sep. 30, 2010		Sep. 30, 2011 segments		Sep. 30, 2010 segments
Number of operating segments					3		3
Number of reportable segments					3		3
Total revenues	$ 3,506.5		$ 3,273.9		$ 10,153.9		$ 9,214.8
Total segment income	134.4	[1]	110.1	[1]	396.7	[1]	331.7	[1]
Other interest expense	(16.4)		(16.1)		(48.6)		(39.8)
Loss on debt extinguishment	0		0		0		(19.6)
Interest income	0		0.3		0.6		0.8
Other losses, net	2.4		0.7		0.2		1.1
INCOME FROM CONTINUING OPERATIONS BEFORE INCOME TAXES	115.6		93.6		348.5		272.0
Domestic [Member]
Total revenues	1,204.4		1,102.6		3,445.5		3,048.7
Total segment income	46.7	[1]	42.5	[1]	135.8	[1]	116.1	[1]
Import [Member]
Total revenues	1,318.3		1,275.1		3,829.0		3,523.9
Total segment income	65.0	[1]	51.3	[1]	187.9	[1]	153.6	[1]
Premium Luxury [Member]
Total revenues	948.7		863.3		2,768.5		2,546.3
Total segment income	49.5	[1]	47.7	[1]	161.3	[1]	142.8	[1]
Corporate and Other [Member]
Total revenues	35.1		32.9		110.9		95.9
Total segment income	$ (26.8)	[1]	$ (31.4)	[1]	$ (88.3)	[1]	$ (80.8)	[1]

[1] * Segment income (loss) is defined as operating income less floorplan interest expense.