Earnings Per Common Share (EPS) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Basic and diluted:
Income from continuing operations	$ 1,250	$ 1,235	$ 3,845	$ 3,707
Earnings allocated to participating share awards	(14)	(15)	(42)	(44)
Income from discontinued operations, net of tax	0	0	0	36
Net income attributable to common shareholders	1,236	1,220	3,803	3,699
Denominator:
Basic: Weighted-average common stock	1,126	1,175	1,143	1,184
Add: weighted-average stock options	6	6	6	7
Diluted	1,132	1,181	1,149	1,191
Earnings Per Share, Basic [Abstract]
Income from continuing operations attributable to common shareholders	$ 1.10	$ 1.04	$ 3.33	$ 3.09
Income from discontinued operations	$ 0	$ 0	$ 0	$ 0.03
Net income attributable to common shareholders	$ 1.10	$ 1.04	$ 3.33	$ 3.12
Earnings Per Share, Diluted [Abstract]
Income from continuing operations attributable to common shareholders	$ 1.09	$ 1.03	$ 3.31	$ 3.08
Income from discontinued operations	$ 0	$ 0	$ 0	$ 0.03
Net income attributable to common shareholders	$ 1.09	$ 1.03	$ 3.31	$ 3.11
Earnings Per Common Share Eps 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	8	19	8	19