Fair Value of Assets and Liabilities Measurement Using Unobservable Input Or Level 3 (Detail) (Significant Unobservable Inputs (Level 3), USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011
Commodity derivatives
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ (1,654)	$ (1,954)
Total gains (losses) included in earnings (or change in net assets) for the period	525	256
Sales	0	0
Settlements	56	146
Transfers in and out of Level 3		0
Ending balance	(1,073)	(1,552)
Interest rate derivatives
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	0	(69)
Total gains (losses) included in earnings (or change in net assets) for the period	4	21
Sales	(6)	(6)
Settlements	0	0
Transfers in and out of Level 3		54	[1]
Ending balance	(2)	0
Foreign currency derivatives
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	0	(43)
Total gains (losses) included in earnings (or change in net assets) for the period	0	0
Sales	0	0
Settlements	0	0
Transfers in and out of Level 3		43	[1]
Ending balance	0	0
Debt Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	0	(1,371)
Total gains (losses) included in earnings (or change in net assets) for the period	0	0
Sales	0	0
Settlements	0	0
Transfers in and out of Level 3		1,371	[1]
Ending balance	$ 0	$ 0

[1] The values related to interest rate and cross currency swaps were transferred from Level 3 to Level 2 as a result of our ability to use data readily available in the public market to corroborate our estimated fair values.