Investments (Equity and Fixed Income Securities, Insurance Contracts and Cash Equivalents in Decommissioning Trust Funds) (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020
Investment Holdings [Line Items]
Fixed income securities Fair Value		$ 2,471
Amortized Cost, Total		4,235	$ 3,846
Total Unrealized Gains		3,815	3,081
Total Unrealized Losses	[1]	(100)	(27)
Fair Value, Total		7,950	6,900
Net assets related to pending purchases of securities		35	49
Fair value of securities in an unrealized loss position		883	293
Virginia Electric and Power Company
Investment Holdings [Line Items]
Fixed income securities Fair Value		1,182
Amortized Cost, Total		1,997	1,789
Total Unrealized Gains		1,753	1,429
Total Unrealized Losses	[2]	(16)	(21)
Allowance for Credit Losses, Total		0
Fair Value, Total		3,734	3,197
Net assets related to pending purchases of securities			10
Fair value of securities in an unrealized loss position		425	142
Net assets related to pending sale of securities		5
Common/collective trust funds | Fixed Income
Investment Holdings [Line Items]
Fixed income securities Amortized Cost, Total	[3]	168	170
Fixed income securities Total Unrealized Gains	[3]	4	5
Fixed income securities Fair Value	[3]	172	175
Common/collective trust funds | Fixed Income | Virginia Electric and Power Company
Investment Holdings [Line Items]
Fixed income securities Amortized Cost, Total	[3]	53	58
Fixed income securities Fair Value	[3]	53	58
Equity securities: | U.S.
Investment Holdings [Line Items]
Equity securities Amortized Cost	[4]	1,567	1,756
Equity securities Total Unrealized Gains	[4]	3,734	2,948
Equity securities Total Unrealized Losses	[4]	(13)	(24)
Equity securities Fair Value	[4]	5,288	4,680
Equity securities: | U.S. | Virginia Electric and Power Company
Investment Holdings [Line Items]
Equity securities Amortized Cost	[5]	841	929
Equity securities Total Unrealized Gains	[5]	1,720	1,371
Equity securities Total Unrealized Losses	[5]	(11)	(21)
Equity securities Fair Value	[5]	2,550	2,279
Corporate debt instruments | Fixed Income
Investment Holdings [Line Items]
Fixed income securities Amortized Cost, Total	[3]	854	572
Fixed income securities Total Unrealized Gains	[3]	32	58
Fixed income securities Total Unrealized Losses	[3]	(5)	(1)
Fixed income securities Fair Value	[3]	881	629
Corporate debt instruments | Fixed Income | Virginia Electric and Power Company
Investment Holdings [Line Items]
Fixed income securities Amortized Cost, Total	[3]	517	315
Fixed income securities Total Unrealized Gains	[3]	17	33
Fixed income securities Total Unrealized Losses	[3]	(3)
Fixed income securities Fair Value	[3]	531	348
Government Securities | Fixed Income
Investment Holdings [Line Items]
Fixed income securities Amortized Cost, Total	[3]	1,382	1,119
Fixed income securities Total Unrealized Gains	[3]	43	66
Fixed income securities Total Unrealized Losses	[3]	(7)	(1)
Fixed income securities Fair Value	[3]	1,418	1,184
Government Securities | Fixed Income | Virginia Electric and Power Company
Investment Holdings [Line Items]
Fixed income securities Amortized Cost, Total	[3]	584	484
Fixed income securities Total Unrealized Gains	[3]	16	25
Fixed income securities Total Unrealized Losses	[3]	(2)
Fixed income securities Fair Value	[3]	598	509
Insurance Contracts | Fixed Income
Investment Holdings [Line Items]
Fixed income securities Amortized Cost, Total		255	237
Fixed income securities Fair Value		255	237
Cash equivalents and other
Investment Holdings [Line Items]
Cash equivalents and other, Amortized Cost	[6]	9	(8)
Cash equivalents and other, Total Unrealized Gains	[6]	2	4
Cash equivalents and other, Total Unrealized Losses	[6]	(75)	(1)
Cash equivalents and other, Fair Value	[6]	(64)	(5)
Cash equivalents and other | Virginia Electric and Power Company
Investment Holdings [Line Items]
Cash equivalents and other, Total Unrealized Gains	[7]	0	0
Cash equivalents and other, Total Unrealized Losses	[7]	0	0
Cash equivalents and other, Allowance for Credit Losses	[7]	0	0
Cash equivalents and other, Amortized Cost	[7]	2	3
Cash equivalents and other, Fair Value	[7]	$ 2	$ 3

[1] The fair value of securities in an unrealized loss position was $883 million and $293 million at December 31, 2021 and 2020, respectively.

[2] The fair value of securities in an unrealized loss position was $425 million and $142 million at December 31, 2021 and 2020, respectively.

[3] Unrealized gains and losses on fixed income securities are included in AOCI and the nuclear decommissioning trust regulatory liability as discussed in Note 2. Changes in allowance for credit losses are included in other income.

[4] Unrealized gains and losses on equity securities are included in other income and the nuclear decommissioning trust regulatory liability as discussed in Note 2.

[5] Unrealized gains and losses on equity securities are included in other income and the nuclear decommissioning trust regulatory liability as discussed in Note 2

[6] Includes pending purchases of securities of $35 million and $49 million at December 31, 2021 and 2020, respectively.

[7] Includes pending sales of securities of $5 million at December 31, 2021, and pending purchases of securities of $10 million at December 31, 2020