Investments (Equity and Fixed Income Securities, Insurance Contracts and Cash Equivalents in Decommissioning Trust Funds) (Detail) - USD ($) $ in Millions		9 Months Ended	12 Months Ended
		Sep. 30, 2021	Dec. 31, 2020
Investment Holdings [Line Items]
Fixed income securities Fair Value		$ 2,523
Amortized Cost, Total		4,207	$ 3,846
Total Unrealized Gains		3,339	3,081
Total Unrealized Losses	[1]	(40)	(27)
Allowance for Credit Losses, Total		0	0
Fair Value, Total		7,506	6,900	[2]
Net assets related to pending purchases of securities		48	49
Fair value of securities in an unrealized loss position		846	293
Virginia Electric and Power Company
Investment Holdings [Line Items]
Fixed income securities Fair Value		1,193
Amortized Cost, Total		1,986	1,789
Total Unrealized Gains		1,534	1,429
Total Unrealized Losses	[3]	(13)	(21)
Allowance for Credit Losses, Total		0	0
Fair Value, Total		3,507	3,197	[4]
Net assets related to pending purchases of securities		2	10
Fair value of securities in an unrealized loss position		397	142
Common/collective trust funds | Fixed Income
Investment Holdings [Line Items]
Fixed income securities Amortized Cost, Total	[5]	187	170
Fixed income securities Total Unrealized Gains	[5]	5	5
Fixed income securities Total Unrealized Losses	[5]	0	0
Fixed income securities Allowance for Credit Losses	[5]	0	0
Fixed income securities Fair Value	[5]	192	175
Common/collective trust funds | Fixed Income | Virginia Electric and Power Company
Investment Holdings [Line Items]
Fixed income securities Amortized Cost, Total	[5]	54	58
Fixed income securities Total Unrealized Gains	[5]	0	0
Fixed income securities Total Unrealized Losses	[5]	0	0
Fixed income securities Allowance for Credit Losses	[5]	0	0
Fixed income securities Fair Value	[5]	54	58
Equity securities: | U.S.
Investment Holdings [Line Items]
Equity securities Amortized Cost	[6]	1,546	1,756
Equity securities Total Unrealized Gains	[6]	3,247	2,948
Equity securities Total Unrealized Losses	[6]	(11)	(24)
Equity securities Fair Value	[6]	4,782	4,680
Equity securities: | U.S. | Virginia Electric and Power Company
Investment Holdings [Line Items]
Equity securities Amortized Cost	[6]	829	929
Equity securities Total Unrealized Gains	[6]	1,497	1,371
Equity securities Total Unrealized Losses	[6]	(10)	(21)
Equity securities Fair Value	[6]	2,316	2,279
Corporate debt instruments | Fixed Income
Investment Holdings [Line Items]
Fixed income securities Amortized Cost, Total	[5]	842	572
Fixed income securities Total Unrealized Gains	[5]	40	58
Fixed income securities Total Unrealized Losses	[5]	(3)	(1)
Fixed income securities Allowance for Credit Losses	[5]	0	0
Fixed income securities Fair Value	[5]	879	629
Corporate debt instruments | Fixed Income | Virginia Electric and Power Company
Investment Holdings [Line Items]
Fixed income securities Amortized Cost, Total	[5]	497	315
Fixed income securities Total Unrealized Gains	[5]	21	33
Fixed income securities Total Unrealized Losses	[5]	(1)	0
Fixed income securities Allowance for Credit Losses	[5]	0	0
Fixed income securities Fair Value	[5]	517	348
Government Securities | Fixed Income
Investment Holdings [Line Items]
Fixed income securities Amortized Cost, Total	[5]	1,414	1,119
Fixed income securities Total Unrealized Gains	[5]	44	66
Fixed income securities Total Unrealized Losses	[5]	(6)	(1)
Fixed income securities Allowance for Credit Losses	[5]	0	0
Fixed income securities Fair Value	[5]	1,452	1,184
Government Securities | Fixed Income | Virginia Electric and Power Company
Investment Holdings [Line Items]
Fixed income securities Amortized Cost, Total	[5]	608	484
Fixed income securities Total Unrealized Gains	[5]	16	25
Fixed income securities Total Unrealized Losses	[5]	(2)
Fixed income securities Allowance for Credit Losses	[5]	0	0
Fixed income securities Fair Value	[5]	622	509
Insurance Contracts
Investment Holdings [Line Items]
Fixed income securities Amortized Cost, Total		246	237
Fixed income securities Total Unrealized Gains			0
Fixed income securities Total Unrealized Losses			0
Fixed income securities Fair Value		246	237
Cash equivalents and other
Investment Holdings [Line Items]
Cash equivalents and other, Amortized Cost	[7]	(28)	(8)
Cash equivalents and other, Total Unrealized Gains	[7]	3	4
Cash equivalents and other, Total Unrealized Losses	[7]	(20)	(1)
Cash equivalents and other, Allowance for Credit Losses	[7]	0	0
Cash equivalents and other, Fair Value	[7]	(45)	(5)
Cash equivalents and other | Virginia Electric and Power Company
Investment Holdings [Line Items]
Cash equivalents and other, Amortized Cost	[8]	(2)	3
Cash equivalents and other, Allowance for Credit Losses	[8]	0	0
Cash equivalents and other, Fair Value	[8]	$ (2)	$ 3

[1] The fair value of securities in an unrealized loss position was $846 million and $293 million at September 30, 2021 and December 31, 2020, respectively.

[2] Dominion Energy’s Consolidated Balance Sheet at December 31, 2020 has been derived from the audited Consolidated Balance Sheet at that date.

[3] The fair value of securities in an unrealized loss position was $397 million and $142 million at September 30, 2021 and December 31, 2020, respectively.

[4] Virginia Power’s Consolidated Balance Sheet at December 31, 2020 has been derived from the audited Consolidated Balance Sheet at that date.

[5] Unrealized gains and losses on fixed income securities are included in AOCI and the nuclear decommissioning trust regulatory liability. Changes in allowance for credit losses are included in other income.

[6] Unrealized gains and losses on equity securities are included in other income and the nuclear decommissioning trust regulatory liability.

[7] Includes pending purchases of securities of $48 million and $49 million at September 30, 2021 and December 31, 2020, respectively.

[8] Includes pending purchases of securities of $2 million and $10 million at September 30, 2021 and December 31, 2020, respectively.