Variable Interest Entities (Pipeline Investments) (Details) - Variable Interest Entity, Not Primary Beneficiary [Member] - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2017	Dec. 31, 2016
Variable Interest Entities [Line Items]
Investments in Joint Ventures	$ 938	$ 751
Atlantic Coast Pipeline [Member]
Variable Interest Entities [Line Items]
Variable Interest Entity Ownership Interest	47.00%
Investments in Joint Ventures	$ 403	265
Sabal Trail Transmission Pipeline [Member]
Variable Interest Entities [Line Items]
Variable Interest Entity Ownership Interest	7.50%
Investments in Joint Ventures	$ 188	140
Constitution Pipeline [Member]
Variable Interest Entities [Line Items]
Variable Interest Entity Ownership Interest	24.00%
Investments in Joint Ventures	$ 82	82
Pipeline Investments [Member]
Variable Interest Entities [Line Items]
Investments in Joint Ventures	673	487
Piedmont Natural Gas [Member]
Variable Interest Entities [Line Items]
Investments in Joint Ventures	$ 152	139
Piedmont Natural Gas [Member] \| Atlantic Coast Pipeline [Member]
Variable Interest Entities [Line Items]
Variable Interest Entity Ownership Interest	7.00%
Investments in Joint Ventures	$ 59	46
Piedmont Natural Gas [Member] \| Constitution Pipeline [Member]
Variable Interest Entities [Line Items]
Variable Interest Entity Ownership Interest	24.00%
Investments in Joint Ventures	$ 93	93
Piedmont Natural Gas [Member] \| Pipeline Investments [Member]
Variable Interest Entities [Line Items]
Investments in Joint Ventures	$ 152	$ 139

Total investments in (A) an entity in which the entity has significant influence, but does not have control, (B) subsidiaries that are not required to be consolidated and are accounted for using the equity and or cost method, and (C) an entity in which the reporting entity shares control of the entity with another party or group. Includes long-term advances receivable from a party that is affiliated with the reporting entity by means of direct or indirect ownership.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.12)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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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.

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Percentage of the Variable Interest Entity's (VIE) voting interest owned by (or beneficial interest in) the reporting entity (directly or indirectly).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 5A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=64801991&loc=SL6759159-111685

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