Derivatives and Other Financial Instruments - Schedule of Reconciliation of Activity for Derivative Contracts (Detail) $ in Millions	3 Months Ended
Mar. 31, 2021 USD ($)
Power Contract [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value measurement, Liabilities, Beginning balance	$ 814
Other comprehensive (loss) income (unrealized)	273
Fair value measurement, Liabilities, Ending balance	1,047
Power Contract [Member] \| Sales [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value measurement, Liabilities	(40)
Financial Contracts [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value measurement, Liabilities, Beginning balance	1
Fair value measurement, Liabilities, Cost of goods sold	(15)
Other comprehensive (loss) income (unrealized)	27
Fair value measurement, Liabilities, Other	2
Fair value measurement, Liabilities, Ending balance	15
Embedded Credit Derivative [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value measurement, Liabilities, Beginning balance	23
Fair value measurement, Liabilities, Other	1
Fair value measurement, Liabilities, Ending balance	18
Embedded Credit Derivative [Member] \| Other Income, Net [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value measurement, Liabilities	(6)
Fair value measurement, Liabilities, Other income, net	$ (5)

Fair value liabilities measured on recurring basis gain loss included in other income, net.

No definition available.

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- Definition

Fair value measurement with unobservable inputs reconciliation recurring basis liabilities gain loss included in cost of goods sold.

+ References

No definition available.

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- Definition

Fair value measurement with unobservable inputs reconciliation recurring basis liabilities increase decrease other.

+ References

No definition available.

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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.

+ References

No definition available.

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- Definition

Amount of gain (loss) recognized in income from liability measured at fair value on recurring basis using unobservable input (level 3).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

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- Definition

Amount of gain (loss) recognized in other comprehensive income (OCI) from liability measured at fair value on recurring basis using unobservable input (level 3).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1a)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

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- Definition

Fair value of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
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