Common Stock (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2012		Mar. 31, 2011
Reconciliation of basic and diluted earnings per share of common stock [Abstract]
Numerator - net income	$ 461		$ 268
Denominator:
Weighted-average number of common shares outstanding - basic (in shares)	412.3		415.8
Performance share awards, options, restricted stock and equity units (in shares)	2.4	[1]	2.6	[1]
Weighted-average number of common shares outstanding - assuming dilution (in shares)	414.7		418.4
Earnings per share of common stock:
Basic (in dollars per share)	$ 1.12		$ 0.64
Assuming dilution (in dollars per share)	$ 1.11		$ 0.64
Antidilutive securities (in shares)	0.6		14.3

[1] Performance share awards are included in diluted weighted-average number of common shares outstanding based upon what would be issued if the end of the reporting period was the end of the term of the award. Performance share awards, options, restricted stock and equity units are included in diluted weighted-average number of common shares outstanding by applying the treasury stock method.