Derivatives and Other Financial Instruments - Schedule of Fair Values of Level 3 Derivative Instruments Recorded as Assets and Liabilities (Detail) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Derivative Instruments Gain Loss [Line Items]
Total asset derivatives	$ 134	$ 14
Total liability derivatives	200	274
Total liability derivatives	1,026	1,048
Level 3 [Member] | Energy Contracts [Member]
Derivative Instruments Gain Loss [Line Items]
Total asset derivatives	52	2
Total liability derivatives	1,212	1,293
Level 3 [Member] | Energy Contracts [Member] | Derivatives Not Designated as Hedging Instruments [Member]
Derivative Instruments Gain Loss [Line Items]
Total asset derivatives	32	2
Total liability derivatives	0	3
Level 3 [Member] | Energy Contracts [Member] | Derivatives Not Designated as Hedging Instruments [Member] | Financial Contracts [Member]
Derivative Instruments Gain Loss [Line Items]
Total asset derivatives	32	2
Level 3 [Member] | Energy Contracts [Member] | Derivatives Not Designated as Hedging Instruments [Member] | Embedded Credit Derivative [Member]
Derivative Instruments Gain Loss [Line Items]
Total liability derivatives	0	1
Total liability derivatives	0	2
Level 3 [Member] | Energy Contracts [Member] | Derivatives Designated as Hedging Instruments [Member]
Derivative Instruments Gain Loss [Line Items]
Total asset derivatives	20	0
Total liability derivatives	1,212	1,290
Level 3 [Member] | Energy Contracts [Member] | Derivatives Designated as Hedging Instruments [Member] | Financial Contracts [Member]
Derivative Instruments Gain Loss [Line Items]
Total asset derivatives	20	0
Level 3 [Member] | Energy Contracts [Member] | Derivatives Designated as Hedging Instruments [Member] | Power Contract [Member]
Derivative Instruments Gain Loss [Line Items]
Total liability derivatives	195	262
Total liability derivatives	$ 1,017	$ 1,028