Stockholders' Equity (Narrative) (Details) (USD $) Share data in Millions	1 Months Ended				3 Months Ended		6 Months Ended
	Aug. 31, 2011	Apr. 30, 2011	Apr. 30, 2010	Apr. 30, 2009	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Stockholders' Equity Note [Abstract]
Amount of common stock repurchases authorized	$ 400,000,000			$ 100,000,000
Increase in stock repurchase authorized amount	250,000,000	150,000,000	150,000,000
Shares repurchased during period					1.5	0.5	2.6	1.4
Value of shares repurchased during period					50,500,000	20,400,000	93,300,000	42,300,000
Remaining amount available for future purchases of shares under approved repurchase program.							111,100,000
Additional stock-based compensation					$ 1,900,000	$ 1,830,000	$ 4,000,000	$ 3,700,000