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		Sep. 30, 2017	Dec. 31, 2016
Investment Holdings [Line Items]
Amortized Cost, Total		$ 3,179	$ 3,053
Total Unrealized Gains	[1]	1,707	1,443
Total Unrealized Losses	[1],[2]	(5)	(12)
Fair Value		4,881	4,484
Net assets related to pending sales and purchases of securities		4	9
Fair value of securities in an unrealized loss position		402	576
Cost method investments
Investment Holdings [Line Items]
Amortized Cost, Other Investments		67	69
Total Unrealized Gains	[1]	0	0
Total Unrealized Losses	[1]	0	0
Fair Value		67	69
Cash equivalents and other
Investment Holdings [Line Items]
Amortized Cost, Other Investments	[3]	5	12
Total Unrealized Gains	[1],[3]	0	0
Total Unrealized Losses	[1],[3]	0	0
Fair Value	[3]	5	12
Common/collective trust funds
Investment Holdings [Line Items]
Amortized Cost, Marketable Securities		66	67
Total Unrealized Gains	[1]	0	0
Total Unrealized Losses	[1]	0	0
Fair Value		66	67
Corporate debt instruments
Investment Holdings [Line Items]
Amortized Cost, Marketable Securities		438	478
Total Unrealized Gains	[1]	15	13
Total Unrealized Losses	[1]	(1)	(4)
Fair Value		452	487
Government securities
Investment Holdings [Line Items]
Amortized Cost, Marketable Securities		1,041	978
Total Unrealized Gains	[1]	28	22
Total Unrealized Losses	[1]	(4)	(8)
Fair Value		1,065	992
Virginia Electric and Power Company
Investment Holdings [Line Items]
Amortized Cost, Total		1,532	1,473
Total Unrealized Gains	[1]	762	639
Total Unrealized Losses	[1],[4]	(2)	(6)
Fair Value		2,292	2,106
Net assets related to pending sales and purchases of securities		(2)	7
Fair value of securities in an unrealized loss position		165	287
Virginia Electric and Power Company | Cost method investments
Investment Holdings [Line Items]
Amortized Cost, Other Investments		67	69
Total Unrealized Gains	[1]	0	0
Total Unrealized Losses	[1]	0	0
Fair Value		67	69
Virginia Electric and Power Company | Cash equivalents and other
Investment Holdings [Line Items]
Amortized Cost, Other Investments	[5]	(2)	7
Total Unrealized Gains	[1],[5]	0	0
Total Unrealized Losses	[1],[5]	0	0
Fair Value	[5]	(2)	7
Virginia Electric and Power Company | Common/collective trust funds
Investment Holdings [Line Items]
Amortized Cost, Marketable Securities		29	26
Total Unrealized Gains	[1]	0	0
Total Unrealized Losses	[1]	0	0
Fair Value		29	26
Virginia Electric and Power Company | Corporate debt instruments
Investment Holdings [Line Items]
Amortized Cost, Marketable Securities		226	274
Total Unrealized Gains	[1]	8	6
Total Unrealized Losses	[1]	0	(4)
Fair Value		234	276
Virginia Electric and Power Company | Government securities
Investment Holdings [Line Items]
Amortized Cost, Marketable Securities		483	420
Total Unrealized Gains	[1]	13	9
Total Unrealized Losses	[1]	(2)	(2)
Fair Value		494	427
U.S. | Equity securities
Investment Holdings [Line Items]
Amortized Cost, Marketable Securities		1,562	1,449
Total Unrealized Gains	[1]	1,664	1,408
Total Unrealized Losses	[1]	0	0
Fair Value		3,226	2,857
U.S. | Virginia Electric and Power Company | Equity securities
Investment Holdings [Line Items]
Amortized Cost, Marketable Securities		729	677
Total Unrealized Gains	[1]	741	624
Total Unrealized Losses	[1]	0	0
Fair Value		$ 1,470	$ 1,301

[1] Included in AOCI and the nuclear decommissioning trust regulatory liability.

[2] The fair value of securities in an unrealized loss position was $402 million and $576 million at September 30, 2017 and December 31, 2016, respectively.

[3] Includes net pending sales of securities of $4 million and $9 million at September 30, 2017 and December 31, 2016, respectively.

[4] The fair value of securities in an unrealized loss position was $165 million and $287 million at September 30, 2017 and December 31, 2016, respectively.

[5] Includes pending purchases of securities of $2 million and pending sales of securities of $7 million at September 30, 2017 and December 31, 2016, respectively.