Stockholders' Equity (Narrative) (Details) (USD $) In Millions	1 Months Ended				3 Months Ended		9 Months Ended
	Aug. 31, 2011	Apr. 30, 2011	Apr. 30, 2010	Apr. 30, 2009	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Stockholders' Equity Note [Abstract]
Amount of common stock repurchases authorized	$ 400.0			$ 100.0
Increase in stock repurchase authorized amount	250.0	150.0	150.0
Shares repurchased during period (shares)					6.8	0.5	9.4	1.9
Value of shares repurchased during period					155.1	22.7	248.4	65.1
Remaining amount available for future purchases of shares under approved repurchase program.							206.0
Additional stock-based compensation					$ 1.6	$ 1.8	$ 5.6	$ 5.5