Investments in Unconsolidated Affiliates (Gas Utilities and Infrastructure Investments) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Schedule of Equity Method Investments [Line Items]
Equity Method Investments	$ 925	$ 499
Gas Utilities and Infrastructure [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investments	$ 566	113
Atlantic Coast Pipeline [Member] \| Gas Utilities and Infrastructure [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	47.00%
Equity Method Investments	$ 265	52
Sabal Trail Transmission Pipeline [Member] \| Gas Utilities and Infrastructure [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	7.50%
Equity Method Investments	$ 140	$ 61
Constitution Pipeline [Member] \| Gas Utilities and Infrastructure [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	24.00%
Equity Method Investments	$ 82
Cardinal Pipeline Company, LLC [Member] \| Gas Utilities and Infrastructure [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	21.49%
Equity Method Investments	$ 16
Pine Needle LNG Company, LLC [Member] \| Gas Utilities and Infrastructure [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	45.00%
Equity Method Investments	$ 16
Hardy Storage Company, LLC [Member] \| Gas Utilities and Infrastructure [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	50.00%
Equity Method Investments	$ 47

The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=66011266&loc=d3e33918-111571

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=66022249&loc=d3e33749-111570

Reference 2: 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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