Income Taxes (Narrative) (Details) - Virginia Electric and Power Company - USD ($) $ in Millions	1 Months Ended	9 Months Ended
Jun. 30, 2017	Sep. 30, 2017
Operating Loss Carryforwards [Line Items]
Open tax year		through 2011
Decrease in unrecognized tax benefits	$ 8
Recognized state tax benefit impacted the effective tax rate	2
Realized interest income	$ 11

Amount of current state and local tax expense (benefit) pertaining to income (loss) from continuing operations.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(h))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 9
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32639-109319

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 6.I.7)
-URI http://asc.fasb.org/extlink&oid=34349781&loc=d3e330036-122817

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration