Earnings Per Common Share (EPS) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Basic and diluted:
Net income	$ 1,529	$ 1,405	$ 2,961	$ 2,685
Earnings allocated to participating share awards	(12)	(13)	(24)	(24)
Net income attributable to common shareholders	1,517	1,392	2,937	2,661
Denominator:
Basic	1,052	1,090	1,056	1,094
Add: Weighted-average stock options	6	7	6	7
Diluted	1,058	1,097	1,062	1,101
Earnings Per Common Share, Basic [Abstract]
Income from continuing operations attributable to common shareholders	$ 1.44	$ 1.28	$ 2.78	$ 2.43
Earnings Per Common Share, Diluted [Abstract]
Income from continuing operations attributable to common shareholders	$ 1.43	$ 1.27	$ 2.77	$ 2.42
Earnings Per Common Share (Textuals) [Abstract]
Subordinated debentures	$ 750	$ 750	$ 750	$ 750
Subordinated debt issuance year	2006	2006	2006	2006
Subordinated debt maturity year	2036	2036	2036	2036
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	0.2	0.2	0.2