Derivatives and Other Financial Instruments - Schedule of Fair Values of Level 3 Derivative Instruments Recorded as Assets and Liabilities (Detail) - Level 3 [Member] - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Derivative Instruments Gain Loss [Line Items]
Total Asset Derivatives	$ 2	$ 0
Total Liability Derivatives	1,293	838
Derivatives Not Designated as Hedging Instruments [Member]
Derivative Instruments Gain Loss [Line Items]
Total Asset Derivatives	2	0
Total Liability Derivatives	3	23
Derivatives Not Designated as Hedging Instruments [Member] | Fair Value of Derivative Contracts - Current [Member] | Financial Contracts [Member]
Derivative Instruments Gain Loss [Line Items]
Total Asset Derivatives	2	0
Derivatives Not Designated as Hedging Instruments [Member] | Fair Value of Derivative Contracts - Current [Member] | Embedded Credit Derivative [Member]
Derivative Instruments Gain Loss [Line Items]
Total Liability Derivatives	1	4
Derivatives Not Designated as Hedging Instruments [Member] | Fair Value of Derivative Contracts - Noncurrent [Member] | Embedded Credit Derivative [Member]
Derivative Instruments Gain Loss [Line Items]
Total Liability Derivatives	2	19
Derivatives Designated as Hedging Instruments [Member]
Derivative Instruments Gain Loss [Line Items]
Total Liability Derivatives	1,290	815
Derivatives Designated as Hedging Instruments [Member] | Fair Value of Derivative Contracts - Current [Member] | Financial Contracts [Member]
Derivative Instruments Gain Loss [Line Items]
Total Liability Derivatives	0	1
Derivatives Designated as Hedging Instruments [Member] | Fair Value of Derivative Contracts - Current [Member] | Power Contract [Member]
Derivative Instruments Gain Loss [Line Items]
Total Liability Derivatives	262	94
Derivatives Designated as Hedging Instruments [Member] | Fair Value of Derivative Contracts - Noncurrent [Member] | Power Contract [Member]
Derivative Instruments Gain Loss [Line Items]
Total Liability Derivatives	$ 1,028	$ 720