Computation of Earnings Per Share (Details) (USD $) In Millions, except Share data in Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Net income available to common shareholders	$ 510	$ 307	$ 941	$ 532
Weighted average number of common shares	698,579	696,625	698,132	695,971
Basic earnings per share	$ 0.73	$ 0.44	$ 1.35	$ 0.76
Weighted average number of shares outstanding, diluted	708,454	704,969	707,990	704,583
Diluted earnings per share	$ 0.72	$ 0.44	$ 1.33	$ 0.76
Earnings Per Share, Basic [Member]
Net income available to common shareholders	510	307	941	532
Weighted average number of common shares	698,579	696,625	698,132	695,971
Basic earnings per share	$ 0.73	$ 0.44	$ 1.35	$ 0.76
Earnings Per Share, Diluted [Member]
Weighted average number of common shares	698,579	696,625	698,132	695,971
Net income available to common shareholders	$ 510	$ 307	$ 941	$ 532
Effect of dilutive outstanding equity-based awards	9,875	8,344	9,858	8,612
Weighted average number of shares outstanding, diluted	708,454	704,969	707,990	704,583
Diluted earnings per share	$ 0.72	$ 0.44	$ 1.33	$ 0.76