Investments (Portion of Unrealized Gains and Losses Relates to Equity Securities) (Detail) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Debt Securities, Available-for-Sale [Line Items]
Net gains (losses) recognized during the period		$ 282	$ (150)	$ 919	$ 370
Less: Net (gains) losses recognized during the period on securities sold during the period		5	1	1	4
Unrealized gains (losses) recognized during the period on securities still held at period end	[1]	287	(149)	920	374
Virginia Electric and Power Company
Debt Securities, Available-for-Sale [Line Items]
Net gains (losses) recognized during the period		145	(80)	473	189
Less: Net (gains) losses recognized during the period on securities sold during the period		3	(1)	(2)	2
Unrealized gains (losses) recognized during the period on securities still held at period end	[1]	$ 148	$ (81)	$ 471	$ 191

[1] Included in other income (expense) and the nuclear decommissioning trust regulatory liability.