Earnings Per Common Share (EPS) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Basic and diluted:
Net income	$ 1,405	$ 1,339	$ 2,685	$ 2,595
Earnings allocated to participating share awards	(13)	(14)	(24)	(28)
Net income attributable to common shareholders	1,392	1,325	2,661	2,567
Denominator:
Basic	1,090	1,145	1,094	1,151
Add: Weighted-average stock options	7	7	7	7
Diluted	1,097	1,152	1,101	1,158
Earnings Per Common Share, Basic [Abstract]
Income from continuing operations attributable to common shareholders	$ 1.28	$ 1.16	$ 2.43	$ 2.23
Earnings Per Common Share, Diluted [Abstract]
Income from continuing operations attributable to common shareholders	$ 1.27	$ 1.15	$ 2.42	$ 2.22
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	0.2	8.0	0.2	8.0