Financial Risk Management Activities - Fair Values of Financial Risk Management Derivative Instruments (Detail) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Derivatives, Fair Value [Line Items]
Assets - Gross fair value of derivative contracts	$ 211	$ 126
Liabilities - Gross fair value of derivative contracts	(29)	(1)
Derivative Contracts Designated as Hedging Instruments:
Derivatives, Fair Value [Line Items]
Assets - Gross fair value of derivative contracts	211	126
Liabilities - Gross fair value of derivative contracts	(29)	0
Derivative Contracts Designated as Hedging Instruments: \| Crude Oil Put Options
Derivatives, Fair Value [Line Items]
Assets - Gross fair value of derivative contracts	205	125
Liabilities - Gross fair value of derivative contracts	0	0
Derivative Contracts Designated as Hedging Instruments: \| Crude Oil Swaps
Derivatives, Fair Value [Line Items]
Assets - Gross fair value of derivative contracts	0
Liabilities - Gross fair value of derivative contracts	(29)
Derivative Contracts Designated as Hedging Instruments: \| Interest Rate Swaps
Derivatives, Fair Value [Line Items]
Assets - Gross fair value of derivative contracts	6	1
Liabilities - Gross fair value of derivative contracts	0	0
Derivative Contracts Not Designated as Hedging Instruments:
Derivatives, Fair Value [Line Items]
Assets - Gross fair value of derivative contracts	0	0
Liabilities - Gross fair value of derivative contracts	0	(1)
Derivative Contracts Not Designated as Hedging Instruments: \| Foreign Exchange Forwards
Derivatives, Fair Value [Line Items]
Assets - Gross fair value of derivative contracts	0	0
Liabilities - Gross fair value of derivative contracts	$ 0	$ (1)

Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and elected not to be offset.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

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- Definition

Fair value, before effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and elected not to be offset.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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