Significant Accounting Policies (Narrative) (Details)	9 Months Ended
Sep. 30, 2016	Sep. 30, 2015
Disposal Group, Disposed of by Sale, Not Discontinued Operations \| Merchant Solar Projects
Subsidiary, Sale of Stock [Line Items]
Percentage of equity interest sold to noncontrolling interest owners	33.00%	33.00%
Four Brothers and Three Cedars
Subsidiary, Sale of Stock [Line Items]
Percentage ownership in total units	50.00%
Dominion Midstream Partners, LP
Subsidiary, Sale of Stock [Line Items]
Ownership interest percentage of limited partner interests	65.00%

The number of units or percentage investment held by one or more members or limited partners of the LLC or LP.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 272
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6373374&loc=d3e70478-108055

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- Definition

The equity interest of noncontrolling shareholders, partners or other equity holders in consolidated entity.

+ References

No definition available.

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- Definition

The parent entity's interest in net assets of the subsidiary, expressed as a percentage.

+ References

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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