Equity (Dividends) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Dividend per share	$ 0.1125	$ 0.1125	$ 0.1125	$ 0.1125	$ 0.0945	$ 0.0945	$ 0.0945	$ 0.0945	$ 0.45	$ 0.378	$ 0.297
Amount									$ 1,233	$ 1,059	$ 850
January [Member]
Dividend per share									$ 0.1125
Amount									312
February [Member]
Dividend per share										$ 0.0945
Amount										267
May [Member]
Dividend per share									$ 0.1125	$ 0.0945
Amount									309	265
July [Member]
Dividend per share									$ 0.1125	$ 0.0945
Amount									307	264
October [Member]
Dividend per share									$ 0.1125	$ 0.0945
Amount									$ 305	$ 263