Financial Risk Management Activities - Gross and Net Fair Values (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Derivatives, Fair Value [Line Items]
Assets - Gross fair value of derivative contracts	$ 69	$ 126
Liabilities - Gross fair value of derivative contracts	(55)	(1)
Gross amount offset in the Consolidate Balance Sheet, Assets	(13)	0
Gross amount offset in the Consolidate Balance Sheet, Liabilities	13	0
Derivative Asset	56	126
Derivative Liability	(42)	(1)
Derivative Contracts Designated as Hedging Instruments
Derivatives, Fair Value [Line Items]
Assets - Gross fair value of derivative contracts	69	126
Liabilities - Gross fair value of derivative contracts	(54)	0
Derivative Contracts Designated as Hedging Instruments \| Put Option
Derivatives, Fair Value [Line Items]
Assets - Gross fair value of derivative contracts	64	125
Liabilities - Gross fair value of derivative contracts	0	0
Derivative Contracts Designated as Hedging Instruments \| Swap
Derivatives, Fair Value [Line Items]
Assets - Gross fair value of derivative contracts	0
Liabilities - Gross fair value of derivative contracts	(54)
Derivative Contracts Designated as Hedging Instruments \| Interest Rate Swaps
Derivatives, Fair Value [Line Items]
Assets - Gross fair value of derivative contracts	5	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	(1)	(1)
Derivative Contracts Not Designated as Hedging Instruments \| Foreign Exchange
Derivatives, Fair Value [Line Items]
Assets - Gross fair value of derivative contracts		0
Liabilities - Gross fair value of derivative contracts	$ (1)	$ (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.

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Fair value of liability associated with 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.

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