Income 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
Earnings Per Share [Abstract]
Net income	$ 569	$ 450	$ 1,378	$ 1,260
Weighted average common shares outstanding, basic	707	706	708	705
Effect of dilutive securities	4	3	4	4
Weighted average common shares outstanding, diluted	711	709	712	709
Basic:
Net income, per basic share	$ 0.80	$ 0.64	$ 1.95	$ 1.79
Diluted:
Net income, per diluted share	$ 0.80	$ 0.63	$ 1.94	$ 1.78
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	4	10	5	10