Debt and Financing Cost - Non-Recurring Fair Value Measurement (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Debt Instrument [Line Items]
Uncommitted credit lines, Carrying Amount	$ 78	$ 91
Commercial paper, Carrying Amount	1,430	489
Notes and debentures, Carrying Amount	11,267	11,765
Total Debt, Carrying Amount	12,775	12,345
Total Debt, Fair Value	13,270	13,920
Uncommitted Credit Lines [Member]
Debt Instrument [Line Items]
Uncommitted credit lines, Carrying Amount	78	91
Total Debt, Fair Value	78	91
Commercial Paper [Member]
Debt Instrument [Line Items]
Total Debt, Fair Value	1,430	489
Notes and Debentures [Member]
Debt Instrument [Line Items]
Total Debt, Fair Value	$ 11,762	$ 13,340