Computation of Earnings Per Share (Details) (USD $) In Millions, except Share data in Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Net income available to common shareholders	$ 469	$ 366	$ 1,410	$ 898
Weighted average number of common shares	699,091	697,052	698,454	696,335
Basic earnings per share	$ 0.67	$ 0.52	$ 2.02	$ 1.29
Weighted average number of shares outstanding, diluted	709,875	705,604	708,439	704,910
Diluted earnings per share	$ 0.66	$ 0.52	$ 1.99	$ 1.27
Earnings Per Share, Basic [Member]
Net income available to common shareholders	469	366	1,410	898
Weighted average number of common shares	699,091	697,052	698,454	696,335
Basic earnings per share	$ 0.67	$ 0.52	$ 2.02	$ 1.29
Earnings Per Share, Diluted [Member]
Weighted average number of common shares	699,091	697,052	698,454	696,335
Net income available to common shareholders	$ 469	$ 366	$ 1,410	$ 898
Effect of dilutive outstanding equity-based awards	10,784	8,552	9,985	8,575
Weighted average number of shares outstanding, diluted	709,875	705,604	708,439	704,910
Diluted earnings per share	$ 0.66	$ 0.52	$ 1.99	$ 1.27