Debt and Financing Cost - Non-Recurring Fair Value Measurement (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Debt Instrument [Line Items]
Uncommitted credit lines, Carrying Amount	$ 57	$ 91
Commercial paper, Carrying Amount		489
Notes and debentures, Carrying Amount	10,868	11,765
Total Debt, Carrying Amount	10,925	12,345
Total Debt, Fair Value	11,315	13,920
Uncommitted Credit Lines [Member]
Debt Instrument [Line Items]
Uncommitted credit lines, Carrying Amount	57	91
Total Debt, Fair Value	57	91
Commercial Paper [Member]
Debt Instrument [Line Items]
Total Debt, Fair Value		489
Notes and Debentures [Member]
Debt Instrument [Line Items]
Total Debt, Fair Value	$ 11,258	$ 13,340