Investments (Fair Value of Fixed Income Securities by Contractual Maturity) (Detail) $ in Millions	Sep. 30, 2021 USD ($)
Schedule of Held-to-maturity Securities [Line Items]
Due in one year or less	$ 351
Due after one year through five years	667
Due after five years through ten years	654
Due after ten years	851
Total	2,523
Virginia Electric and Power Company
Schedule of Held-to-maturity Securities [Line Items]
Due in one year or less	83
Due after one year through five years	354
Due after five years through ten years	372
Due after ten years	384
Total	$ 1,193