Derivatives and Other Financial Instruments - Schedule of Fair Values of Level 3 Derivative Instruments Recorded as Assets and Liabilities (Detail) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Derivative Instruments Gain Loss [Line Items]
Total asset derivatives	$ 22	$ 29
Total liability derivatives	205	214
Total liability derivatives	925	1,092
Level 3 [Member] | Energy Contracts [Member]
Derivative Instruments Gain Loss [Line Items]
Total asset derivatives	12	16
Total liability derivatives	1,120	1,297
Level 3 [Member] | Derivatives Not Designated as Hedging Instruments [Member] | Energy Contracts [Member]
Derivative Instruments Gain Loss [Line Items]
Total asset derivatives	12	16
Level 3 [Member] | Derivatives Not Designated as Hedging Instruments [Member] | Financial Contracts [Member] | Energy Contracts [Member]
Derivative Instruments Gain Loss [Line Items]
Total asset derivatives	12	16
Level 3 [Member] | Derivatives Designated as Hedging Instruments [Member] | Energy Contracts [Member]
Derivative Instruments Gain Loss [Line Items]
Total liability derivatives	1,120	1,297
Level 3 [Member] | Derivatives Designated as Hedging Instruments [Member] | Power Contract [Member] | Energy Contracts [Member]
Derivative Instruments Gain Loss [Line Items]
Total liability derivatives	200	210
Total liability derivatives	$ 920	$ 1,087