Shareholders' Equity (Stock Options Exercised and Restricted Stock Grants) (Details) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Stockholders' Equity Note [Abstract]
Shares issued	1,700,000	4,400,000	3,100,000
Proceeds from the exercise of stock options	$ 32.0	$ 78.7	$ 49.9
Average exercise price per share	$ 19.33	$ 17.74	$ 16.25
Shares issued	160,740	163,892	188,740
Shares surrendered to AutoNation to satisfy tax witholding obligations in connection with the vesting of restricted stock or to pay for an option exercise	81,717	59,452	36,614