Derivatives and Other Financial Instruments - Schedule of Fair Values of Level 3 Derivative Instruments Recorded as Assets and Liabilities (Detail) - USD ($) $ in Millions	Sep. 30, 2022	Dec. 31, 2021
Derivative Instruments Gain Loss [Line Items]
Total Asset Derivatives	$ 207	$ 14
Fair value liability derivatives	167	274
Fair value liability derivatives	812	1,048
Level 3 [Member]
Derivative Instruments Gain Loss [Line Items]
Total Asset Derivatives	63	2
Fair value liability derivatives	944	1,293
Level 3 [Member] | Derivatives Designated as Hedging Instruments [Member]
Derivative Instruments Gain Loss [Line Items]
Total Asset Derivatives	2
Fair value liability derivatives	944	1,290
Level 3 [Member] | Derivatives Designated as Hedging Instruments [Member] | Power Contract [Member]
Derivative Instruments Gain Loss [Line Items]
Total Asset Derivatives	2
Fair value liability derivatives	148	262
Fair value liability derivatives	796	1,028
Level 3 [Member] | Derivatives Not Designated as Hedging Instruments [Member]
Derivative Instruments Gain Loss [Line Items]
Total Asset Derivatives	61	2
Fair value liability derivatives		3
Level 3 [Member] | Derivatives Not Designated as Hedging Instruments [Member] | Embedded Credit Derivative [Member]
Derivative Instruments Gain Loss [Line Items]
Fair value liability derivatives		1
Fair value liability derivatives		2
Level 3 [Member] | Derivatives Not Designated as Hedging Instruments [Member] | Financial Contracts [Member]
Derivative Instruments Gain Loss [Line Items]
Total Asset Derivatives	$ 61	$ 2