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Derivatives and Other Financial Instruments - Schedule of Reconciliation of Activity for Derivative Contracts (Detail) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2021 | Jun. 30, 2021
Power Contract [Member] |  |
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items] |  |
Fair value measurement, Liabilities, Beginning balance | $ 1,047 | $ 814
Other comprehensive (loss) income (unrealized) | 417 | 690
Fair value measurement, Liabilities, Ending balance | 1,397 | 1,397
Power Contract [Member] | Sales [Member] |  |
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items] |  |
Fair value measurement, Liabilities | (67) | (107)
Financial Contracts [Member] |  |
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items] |  |
Fair value measurement, Liabilities, Beginning balance | 15 | 1
Fair value measurement, Liabilities, Cost of goods sold | 7 | (8)
Other comprehensive (loss) income (unrealized) | (21) | 6
Fair value measurement, Liabilities, Other |  | 2
Other comprehensive (loss) income (unrealized) | 2 | 2
Fair value measurement, Assets, Ending balance | 5 | 5
Financial Contracts [Member] | Other Expense (Income), Net [Member] |  |
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items] |  |
Fair value measurement, Liabilities | (1) | (1)
Fair value measurement, Assets | 3 | 3
Financial Contracts [Member] | Other Income, Net [Member] |  |
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items] |  |
Fair value measurement, Liabilities, Other income, net | (1) | (1)
Fair value measurement, Assets, Other income, net | 3 | 3
Embedded Credit Derivative [Member] |  |
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items] |  |
Fair value measurement, Liabilities, Beginning balance | 18 | 23
Fair value measurement, Liabilities, Other | (1) |
Fair value measurement, Liabilities, Ending balance | 18 | 18
Embedded Credit Derivative [Member] | Other Expense (Income), Net [Member] |  |
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items] |  |
Fair value measurement, Liabilities | 1 | (5)
Embedded Credit Derivative [Member] | Other Income, Net [Member] |  |
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items] |  |
Fair value measurement, Liabilities, Other income, net | $ 1 | $ (4)

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