Debt - Additional Information (Detail) (USD $)	Dec. 31, 2012	Dec. 31, 2011
Short And Long Term Debt [Line Items]
Debt financing program through the issuance of commercial paper	$ 3,000,000,000
Amounts of commercial paper outstanding	2,500,000,000	750,000,000
Weighted average yield for commercial paper outstanding	0.20%	0.10%
Revolving credit facility expiration date	2016-07
Revolving credit facility, amount outstanding	0	0
Short-term debt	2,549,000,000	1,218,000,000
Estimated fair value of long-term debt	3,200,000,000	3,200,000,000
1.25% Notes due on May 19, 2014
Short And Long Term Debt [Line Items]
Secured promissory note, interest rate	1.25%	1.25%
Effective interest rate	1.258%
2.125% Notes due on May 19, 2016
Short And Long Term Debt [Line Items]
Secured promissory note, interest rate	2.125%	2.125%
Effective interest rate	2.241%
3.625% Notes due on May 19, 2021
Short And Long Term Debt [Line Items]
Secured promissory note, interest rate	3.625%	3.625%
Effective interest rate	3.734%
Unsecured Debt
Short And Long Term Debt [Line Items]
Debt instrument, face amount	3,000,000,000	3,000,000,000
Number of unsecured senior notes tranches	3	3
Promissory Notes
Short And Long Term Debt [Line Items]
Short-term debt		468,000,000
Secured promissory note, interest rate		1.00%
Commercial Paper Financing Credit Facility
Short And Long Term Debt [Line Items]
Debt financing program through the issuance of commercial paper	$ 3,000,000,000