Share Repurchase Programs (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended		3 Months Ended		2 Months Ended		6 Months Ended		3 Months Ended		12 Months Ended				1 Months Ended
	Sep. 30, 2011	Dec. 31, 2011	Oct. 31, 2008 Share Repurchase Program July 2008 [Member]	Jul. 31, 2008 Share Repurchase Program July 2008 [Member]	Jul. 31, 2009 Share Repurchase Program May 2009 [Member]	May 31, 2009 Share Repurchase Program May 2009 [Member]	Jan. 31, 2010 Share Repurchase Program July 2009 [Member]	Jul. 27, 2009 Share Repurchase Program July 2009 [Member]	May 21, 2010 Share Repurchase Program Feb 2010 [Member]	Feb. 25, 2010 Share Repurchase Program Feb 2010 [Member]	Aug. 31, 2011 Share Repurchase Program Aug 2010 [Member]	May 31, 2011 Share Repurchase Program Aug 2010 [Member]	May 19, 2011 Share Repurchase Program Aug 2010 [Member]	Aug. 20, 2010 Share Repurchase Program Aug 2010 [Member]	Aug. 31, 2011 Share Repurchase Program Aug 2011 [Member]	Dec. 31, 2011 Share Repurchase Program Aug 2011 [Member]
Share Repurchase Program
Share repurchase program periods			July 2008 - October 2008		May 2009 - July 2009		July 2009 - January 2010		February 2010 - May 2010		August 2010 - August 2011				August 2011
Amount authorized		$ 3,800		$ 400		$ 250		$ 750		$ 250		$ 1,400	$ 1,400	$ 1,000	$ 750	$ 1,400
Number of shares repurchased	42.7		5.9		3.7		9.7		3.3		15.0				5.1