Shareholders' Equity (Details) (USD $) Share data in Millions, except Per Share data, unless otherwise specified	3 Months Ended				1 Months Ended	3 Months Ended	12 Months Ended
	Mar. 31, 2013		Mar. 31, 2012		Apr. 30, 2012 2012 - Share Repurchase Program	Mar. 31, 2013 2012 - Share Repurchase Program	Mar. 31, 2013 2012 - Share Repurchase Program
Common Stock Programs
Share repurchase authorization limit					$ 5,000,000,000
Shares purchased (in shares)						5.0	24.5
Average price per share of stock repurchased						$ 59.82
Total cost of shares purchased	300,000,000					300,000,000	1,300,000,000
Share repurchase, remaining authorization limit						3,700,000,000
Participating Securities
Net income	$ 3,000,000		$ 3,000,000
Weighted average shares outstanding
Shares for basic earnings per share	316.4	[1]	332.4	[1]
Common stock equivalents (in shares)	3.6		4.2
Shares for diluted earnings per share	320.0		336.6
Number of participating securities (in shares)	4.2		4.9
Number of shares excluded from the calculation of diluted earnings per share	0.2		1.0

[1] Includes 4.2 million and 4.9 million of participating securities for the three months ended March 31, 2013 and 2012, respectively.