Investments (Fair Value of Fixed Income Securities by Contractual Maturity) (Detail) $ in Millions	Mar. 31, 2020 USD ($)
Schedule of Held-to-maturity Securities [Line Items]
Due in one year or less	$ 178
Due after one year through five years	430
Due after five years through ten years	389
Due after ten years	750
Total	1,747
Virginia Electric and Power Company
Schedule of Held-to-maturity Securities [Line Items]
Due in one year or less	73
Due after one year through five years	200
Due after five years through ten years	211
Due after ten years	368
Total	$ 852