Investments (Fair Value of Fixed Income Securities by Contractual Maturity) (Detail) $ in Millions	Jun. 30, 2021 USD ($)
Schedule of Held-to-maturity Securities [Line Items]
Due in one year or less	$ 293
Due after one year through five years	673
Due after five years through ten years	677
Due after ten years	894
Total	2,537
Virginia Electric and Power Company
Schedule of Held-to-maturity Securities [Line Items]
Due in one year or less	82
Due after one year through five years	340
Due after five years through ten years	401
Due after ten years	386
Total	$ 1,209