Debt (Additional Information) (Details) (USD $)	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2013 1.25% Notes due on May 19, 2014	Mar. 31, 2013 2.125% Notes due on May 19, 2016	Mar. 31, 2013 3.625% Notes due on May 19, 2021	May 31, 2011 Unsecured debt Loan	Mar. 31, 2013 Commercial paper financing credit facility
Line of Credit Facility [Line Items]
Outstanding Balance Under Revolving Credit Facility	$ 0	$ 0
Debt financing program through the issuance of commercial paper	3,000,000,000						3,000,000,000
Amounts of commercial paper outstanding	2,200,000,000	2,500,000,000
Weighted average yield for commercial paper outstanding	0.20%	0.20%
Line of credit maturity date	2016-07
Debt instrument, face amount						3,000,000,000
Number of unsecured senior notes tranches						3
Effective interest rate			1.258%	2.241%	3.734%
Estimated fair value of long-term debt	$ 3,200,000,000