Earnings per Common Share (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
Numerator:
Net income	$ 316	$ 723	$ 1,459	$ 1,912
Less: Preferred stock dividends	6		6
Net income available to common shareholders	$ 310	$ 723	$ 1,453	$ 1,912
Denominator:
Weighted average common shares outstanding	461.1	485.9	468.2	491.5
Effect of dilutive potential common shares:
Stock options (in shares)	4.2	2.7	3.9	2.2
Restricted stock units and performance stock awards (non-participating) (in shares)	1.8	1.3	1.7	1.0
Weighted average common and dilutive potential common shares outstanding	467.1	489.9	473.8	494.7
Earnings per common share - Basic (in dollars per share)	$ 0.67	$ 1.49	$ 3.10	$ 3.89
Earnings per common share - Diluted (in dollars per share)	$ 0.66	$ 1.48	$ 3.07	$ 3.86
Other Earnings Per Share Disclosures
Antidilutive stock options, exercise price exceeds market price (in shares)	8.4	17.8	13.0	22.1
Antidilutive stock options, exercise price exceeds market price, exercise price range, low end of range (in dollars per share)	$ 41.16	$ 31.41	$ 39.05	$ 26.56
Antidilutive stock options, exercise price exceeds market price, exercise price range, high end of range (in dollars per share)	$ 62.42	$ 62.84	$ 62.42	$ 62.84