Debt and Financing Cost - Non-Recurring Fair Value Measurement (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Debt Instrument [Line Items]
Uncommitted credit lines, Carrying Amount	$ 94	$ 91
Commercial paper, Carrying Amount	619	489
Notes and debentures, Carrying Amount	11,766	11,765
Total Debt, Carrying Amount	12,479	12,345
Total Debt, Fair Value	13,601	13,920
Uncommitted Credit Lines [Member]
Debt Instrument [Line Items]
Uncommitted credit lines, Carrying Amount	94	91
Total Debt, Fair Value	94	91
Commercial Paper [Member]
Debt Instrument [Line Items]
Total Debt, Fair Value	619	489
Notes and Debentures [Member]
Debt Instrument [Line Items]
Total Debt, Fair Value	$ 12,888	$ 13,340