Investments (Fair Value of Fixed Income Securities by Contractual Maturity) (Detail) $ in Millions	Sep. 30, 2020 USD ($)
Schedule of Held-to-maturity Securities [Line Items]
Due in one year or less	$ 194
Due after one year through five years	503
Due after five years through ten years	485
Due after ten years	768
Total	1,950
Virginia Electric and Power Company
Schedule of Held-to-maturity Securities [Line Items]
Due in one year or less	66
Due after one year through five years	234
Due after five years through ten years	268
Due after ten years	314
Total	$ 882