Effect of Derivative Instruments - Balance Sheet Table (Detail) (USD $) In Millions	Sep. 30, 2011	Dec. 31, 2010
Derivatives Fair Value [Line Items]
Gross derivative assets	$ 599	$ 801
Gross derivative liabilities	(1,287)	(724)
Commodity Contract [Member]
Derivatives Fair Value [Line Items]
Gross derivative assets	599	801
Gross derivative liabilities	(115)	(489)
Commodity Contract [Member] | Other Current Assets [Member]
Derivatives Fair Value [Line Items]
Gross derivative assets	428	444
Gross derivative liabilities	(81)	(274)
Commodity Contract [Member] | Other Assets [Member]
Derivatives Fair Value [Line Items]
Gross derivative assets	166	242
Gross derivative liabilities	(9)	(56)
Commodity Contract [Member] | Accrued Expenses [Member]
Derivatives Fair Value [Line Items]
Gross derivative assets	4	89
Gross derivative liabilities	(17)	(131)
Commodity Contract [Member] | Other Liabilities [Member]
Derivatives Fair Value [Line Items]
Gross derivative assets	1	26
Gross derivative liabilities	(8)	(28)
Interest Rate Contract and Other [Member]
Derivatives Fair Value [Line Items]
Gross derivative liabilities	(1,172)	(235)
Interest Rate Contract and Other [Member] | Accrued Expenses [Member]
Derivatives Fair Value [Line Items]
Gross derivative liabilities	(185)	(190)
Interest Rate Contract and Other [Member] | Other Liabilities [Member]
Derivatives Fair Value [Line Items]
Gross derivative liabilities	$ (987)	$ (45)