Investments (Marketable Equity and Debt Securities and Cash Equivalents (Classified as Available-for-sale) and Cost Method Investments in Decommissioning Trust Funds) (Details) - USD ($) $ in Millions		Dec. 31, 2016	Dec. 31, 2015
Investment Holdings [Line Items]
Total Unrealized Gains	[1]	$ 1,443	$ 1,258
Total Unrealized Losses	[1],[2]	(12)	(11)
Nuclear decommissioning trust funds		4,484	4,183
Total Amortized Cost		3,053	2,936
Net assets related to pending sales and purchases of securities		9	12
Fair value of securities in an unrealized loss position		576	592
Virginia Electric and Power Company
Investment Holdings [Line Items]
Other investments and securities, at cost		1,473	1,404
Total Unrealized Gains	[3]	639	548
Total Unrealized Losses	[3],[4]	(6)	(7)
Nuclear decommissioning trust funds		2,106	1,945
Net assets related to pending sales and purchases of securities		7	8
Fair value of securities in an unrealized loss position		287	281
Cost method investments
Investment Holdings [Line Items]
Other investments and securities, at cost		69	70
Total Unrealized Gains	[1]	0	0
Total Unrealized Losses	[1]	0	0
Nuclear decommissioning trust funds		69	70
Cost method investments | Virginia Electric and Power Company
Investment Holdings [Line Items]
Other investments and securities, at cost		69	70
Total Unrealized Gains	[3]	0	0
Total Unrealized Losses	[3]	0	0
Nuclear decommissioning trust funds		69	70
Cash equivalents and other
Investment Holdings [Line Items]
Other investments and securities, at cost	[5]	12	14
Total Unrealized Gains	[1],[5]	0	0
Total Unrealized Losses	[1],[5]	0	0
Nuclear decommissioning trust funds	[5]	12	14
Cash equivalents and other | Virginia Electric and Power Company
Investment Holdings [Line Items]
Amortized Cost	[6]	7	8
Total Unrealized Gains	[3],[6]	0	0
Total Unrealized Losses	[3],[6]	0	0
Nuclear decommissioning trust funds	[6]	7	8
Corporate debt instruments
Investment Holdings [Line Items]
Amortized Cost		478	436
Total Unrealized Gains	[1]	13	11
Total Unrealized Losses	[1]	(4)	(7)
Nuclear decommissioning trust funds		487	440
Corporate debt instruments | Virginia Electric and Power Company
Investment Holdings [Line Items]
Amortized Cost		274	238
Total Unrealized Gains	[3]	6	5
Total Unrealized Losses	[3]	(4)	(5)
Nuclear decommissioning trust funds		276	238
Government securities
Investment Holdings [Line Items]
Amortized Cost		978	962
Total Unrealized Gains	[1]	22	30
Total Unrealized Losses	[1]	(8)	(4)
Nuclear decommissioning trust funds		992	988
Government securities | Virginia Electric and Power Company
Investment Holdings [Line Items]
Amortized Cost		420	421
Total Unrealized Gains	[3]	9	15
Total Unrealized Losses	[3]	(2)	(2)
Nuclear decommissioning trust funds		427	434
Common/collective trust funds
Investment Holdings [Line Items]
Amortized Cost		67	100
Total Unrealized Gains	[1]	0	0
Total Unrealized Losses	[1]	0	0
Nuclear decommissioning trust funds		67	100
Common/collective trust funds | Virginia Electric and Power Company
Investment Holdings [Line Items]
Amortized Cost		26	34
Total Unrealized Gains	[3]	0	0
Total Unrealized Losses	[3]	0	0
Nuclear decommissioning trust funds		26	34
U.S. | Equity securities:
Investment Holdings [Line Items]
Amortized Cost		1,449	1,354
Total Unrealized Gains	[1]	1,408	1,217
Total Unrealized Losses	[1]	0	0
Nuclear decommissioning trust funds		2,857	2,571
U.S. | Equity securities: | Virginia Electric and Power Company
Investment Holdings [Line Items]
Amortized Cost		677	633
Total Unrealized Gains	[3]	624	528
Total Unrealized Losses	[3]	0	0
Nuclear decommissioning trust funds		$ 1,301	$ 1,161

[1] Included in AOCI and the nuclear decommissioning trust regulatory liability as discussed in Note 2.

[2] fair value of securities in an unrealized loss position was $576 million and $592 million at December 31, 2016 and 2015, respectively.

[3] Included in AOCI and the nuclear decommissioning trust regulatory liability as discussed in Note 2.

[4] The fair value of securities in an unrealized loss position was $287 million and $281 million at December 31, 2016 and 2015, respectively.

[5] Includes pending sales of securities of $9 million and $12 million at December 31, 2016 and 2015, respectively.

[6] Includes pending sales of securities of $7 million and $8 million at December 31, 2016 and 2015, respectively.