Derivatives and Hedge Accounting Activities (Fair Value of Derivatives) (Detail) - USD ($) $ in Millions	Sep. 30, 2026	Dec. 31, 2025
Derivatives Fair Value [Line Items]
Total current derivative assets	$ 221	$ 335
Total noncurrent derivative assets	1,189	623
Total derivative assets	1,410	958
Total current derivative liabilities	177	111
Total noncurrent derivative liabilities	247	134
Total derivative liabilities	424	245
Virginia Electric and Power Company
Derivatives Fair Value [Line Items]
Total current derivative assets	43	212
Total noncurrent derivative assets	598	270
Total derivative assets	641	482
Total current derivative liabilities	43	22
Total noncurrent derivative liabilities	12	9
Total derivative liabilities	55	31
Designated as Hedging Instrument \| Interest Rate Contract
Derivatives Fair Value [Line Items]
Total current derivative assets	0	15
Total noncurrent derivative assets	515	184
Total current derivative liabilities	0	0
Total noncurrent derivative liabilities	0	9
Designated as Hedging Instrument \| Interest Rate Contract \| Virginia Electric and Power Company
Derivatives Fair Value [Line Items]
Total current derivative assets	0	15
Total noncurrent derivative assets	480	182
Total current derivative liabilities	0	0
Total noncurrent derivative liabilities	0	8
Fair Value - Derivatives not under Hedge Accounting \| Commodity Contract
Derivatives Fair Value [Line Items]
Total current derivative assets	219	295
Total noncurrent derivative assets	642	434
Total current derivative liabilities	168	98
Total noncurrent derivative liabilities	247	118
Fair Value - Derivatives not under Hedge Accounting \| Commodity Contract \| Virginia Electric and Power Company
Derivatives Fair Value [Line Items]
Total current derivative assets	41	172
Total noncurrent derivative assets	118	85
Total current derivative liabilities	34	12
Total noncurrent derivative liabilities	12	1
Fair Value - Derivatives not under Hedge Accounting \| Interest Rate Contract
Derivatives Fair Value [Line Items]
Total current derivative assets	0	0
Total noncurrent derivative assets	32	2
Total current derivative liabilities	0	3
Total noncurrent derivative liabilities	0	7
Fair Value - Derivatives not under Hedge Accounting \| Foreign currency exchange rate
Derivatives Fair Value [Line Items]
Total current derivative assets	2	25
Total noncurrent derivative assets	0	3
Total current derivative liabilities	9	10
Total noncurrent derivative liabilities	0	0
Fair Value - Derivatives not under Hedge Accounting \| Foreign currency exchange rate \| Virginia Electric and Power Company
Derivatives Fair Value [Line Items]
Total current derivative assets	2	25
Total noncurrent derivative assets	0	3
Total current derivative liabilities	9	10
Total noncurrent derivative liabilities	$ 0	$ 0