Financial Risk Management Activities - Gross and Net Fair Values (Detail) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Derivatives Fair Value [Line Items]
Assets - Gross fair value of derivative contracts	$ 66	$ 1
Assets - Net Fair Value of Derivative Contracts	66	1
Liabilities - Gross fair value of derivative contracts	(13)	(13)
Liabilities - Net Fair Value of Derivative Contracts	(13)	(13)
Derivative Contracts Designated as Hedging Instruments
Derivatives Fair Value [Line Items]
Assets - Gross fair value of derivative contracts	66	0
Liabilities - Gross fair value of derivative contracts	(13)	(11)
Derivative Contracts Designated as Hedging Instruments \| Commodity \| Accounts Receivable and Accounts Payable
Derivatives Fair Value [Line Items]
Assets - Gross fair value of derivative contracts	66
Liabilities - Gross fair value of derivative contracts	(8)
Derivative Contracts Designated as Hedging Instruments \| Commodity \| Accounts Payable
Derivatives Fair Value [Line Items]
Assets - Gross fair value of derivative contracts		0
Liabilities - Gross fair value of derivative contracts		(7)
Derivative Contracts Designated as Hedging Instruments \| Interest Rate \| Other assets (noncurrent) and Accounts Payable
Derivatives Fair Value [Line Items]
Assets - Gross fair value of derivative contracts		0
Liabilities - Gross fair value of derivative contracts		(4)
Derivative Contracts Designated as Hedging Instruments \| Interest Rate \| Other Liabilities and Deferred Credits
Derivatives Fair Value [Line Items]
Assets - Gross fair value of derivative contracts	0
Liabilities - Gross fair value of derivative contracts	$ (5)
Derivative Contracts Not Designated as Hedging Instruments
Derivatives Fair Value [Line Items]
Assets - Gross fair value of derivative contracts		1
Liabilities - Gross fair value of derivative contracts		(2)
Derivative Contracts Not Designated as Hedging Instruments \| Commodity \| Accounts Payable
Derivatives Fair Value [Line Items]
Assets - Gross fair value of derivative contracts		0
Liabilities - Gross fair value of derivative contracts		(2)
Derivative Contracts Not Designated as Hedging Instruments \| Foreign Exchange
Derivatives Fair Value [Line Items]
Assets - Gross fair value of derivative contracts		1
Liabilities - Gross fair value of derivative contracts		$ 0

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.

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Fair value, after the 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 not elected to be offset.

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+ References

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