Employee Benefit Plans (Net Periodic Benefit Cost (Credit)) (Detail) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost		$ 42	$ 43	$ 84	$ 86
Interest cost		79	90	158	181
Expected return on plan assets		(208)	(192)	(416)	(385)
Amortization of prior service cost (credit)			1		1
Amortization of net actuarial loss		49	48	97	97
Settlements	[1]	7	2	5	2
Net periodic benefit credit		(31)	(8)	(72)	(18)
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost		6	7	12	14
Interest cost		12	15	24	30
Expected return on plan assets		(43)	(39)	(87)	(78)
Amortization of prior service cost (credit)		(11)	(13)	(21)	(25)
Amortization of net actuarial loss		1	2	2	3
Net periodic benefit credit		$ (35)	$ (28)	$ (70)	$ (56)

[1] 2021 amounts relate primarily to the Dominion Energy executive nonqualified pension plan.