Earnings Per Common Share (EPS) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Basic and diluted:
Net income	$ 1,366	$ 1,250	$ 4,051	$ 3,845
Earnings allocated to participating share awards	(12)	(14)	(36)	(42)
Net income attributable to common shareholders	1,354	1,236	4,015	3,803
Denominator:
Basic	1,074	1,126	1,087	1,143
Add: Weighted-average stock options	7	6	7	6
Diluted	1,081	1,132	1,094	1,149
Earnings Per Common Share, Basic [Abstract]
Income from continuing operations attributable to common shareholders	$ 1.26	$ 1.10	$ 3.69	$ 3.33
Earnings Per Common Share, Diluted [Abstract]
Income from continuing operations attributable to common shareholders	$ 1.25	$ 1.09	$ 3.67	$ 3.31
Earnings Per Common Share (Textuals) [Abstract]
Subordinated debentures	$ 750	$ 750	$ 750	$ 750
Stock options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per Share, amount	0.1	8.0	0.2	8.0