Variable Interest Entities (Schedule of Non-Consolidated VIE Pipeline Investments) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Variable Interest Entity [Line Items]
Investments in equity method unconsolidated affiliates	$ 925	$ 499
Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Investments in equity method unconsolidated affiliates	$ 751	387
Constitution Pipeline [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage	24.00%
Investments in equity method unconsolidated affiliates	$ 82
Sabal Trail Transmission Pipeline [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage	7.50%
Investments in equity method unconsolidated affiliates	$ 140	$ 61
Atlantic Coast Pipeline [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage	47.00%	40.00%
Investments in equity method unconsolidated affiliates	$ 265	$ 52
Atlantic Coast Pipeline [Member] | Piedmont Natural Gas [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage		7.00%
Pipeline Investments [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Investments in equity method unconsolidated affiliates	$ 487	$ 113