Investments (Fair Value of Fixed Income Securities by Contractual Maturity) (Detail) $ in Millions	Jun. 30, 2020 USD ($)
Schedule of Held-to-maturity Securities [Line Items]
Due in one year or less	$ 212
Due after one year through five years	486
Due after five years through ten years	485
Due after ten years	769
Total	1,952
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	227
Due after five years through ten years	273
Due after ten years	321
Total	$ 900