Subsequent Events (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	1 Months Ended			12 Months Ended	1 Months Ended
	Apr. 30, 2011	Oct. 31, 2008	Feb. 29, 2008	Dec. 31, 2011	Jan. 31, 2012 Dividend Declared [Member]	Apr. 30, 2011 Quarterly [Member] Previous [Member]	Apr. 30, 2011 Quarterly [Member] Subsequent [Member]	Apr. 30, 2011 Annual [Member] Previous [Member]	Apr. 30, 2011 Annual [Member] Subsequent [Member]
Subsequent Event [Line Items]
Subsequent Event, Date					Jan. 05, 2012
Subsequent Event, Description					The cash dividends are for the period from November 1, 2011 to January 31, 2012 and was paid on February 1, 2012 to holders of record as of January 18, 2012.
Subsequent Event, Amount					$ 9
Common Stock, Dividends, Per Share, Declared					$ 0.06	$ 0.05	$ 0.06	$ 0.2	$ 0.24
Common Stock, Dividends, Rate Increase, Percent	20.00%
Share Repurchase Plan, Authorized Repurchase Amount	$ 129	$ 100	$ 400	$ 629