Investments (Fair Value of Fixed Income Securities by Contractual Maturity) (Detail) $ in Millions	Mar. 31, 2021 USD ($)
Schedule of Held-to-maturity Securities [Line Items]
Due in one year or less	$ 292
Due after one year through five years	640
Due after five years through ten years	614
Due after ten years	805
Total	2,351
Virginia Electric and Power Company
Schedule of Held-to-maturity Securities [Line Items]
Due in one year or less	111
Due after one year through five years	314
Due after five years through ten years	365
Due after ten years	312
Total	$ 1,102