Equity - Remaining Value of Authorization under Share Repurchase Programs (Detail) (USD $)	12 Months Ended				2 Months Ended	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Apr. 26, 2011	Feb. 26, 2013 Subsequent Event [Member]	Dec. 31, 2012 Subsequent Event [Member]	Feb. 05, 2013 Subsequent Event [Member]
Additional amount of shares authorized to be repurchased				$ 1,500,000,000			$ 1,500,000,000
Aggregate amount of repurchased shares	(872,000,000)	(958,000,000)	(834,000,000)		(104,000,000)
Remaining value under share repurchase program	$ 262,000,000				$ 1,658,000,000	$ 262,000,000