Investments (Fair Value of Fixed Income Securities by Contractual Maturity) (Detail) $ in Millions	Dec. 31, 2020 USD ($)
Schedule of Held-to-maturity Securities [Line Items]
Due in one year or less	$ 227
Due after one year through five years	506
Due after five years through ten years	505
Due after ten years	750
Total	1,988
Virginia Electric and Power Company
Schedule of Held-to-maturity Securities [Line Items]
Due in one year or less	79
Due after one year through five years	238
Due after five years through ten years	297
Due after ten years	301
Total	$ 915