Variable Interest Entities (Schedule of Non-Consolidated VIE Pipeline Investments) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Variable Interest Entity [Line Items]
Investments in equity method unconsolidated affiliates	$ 1,409	$ 1,175	$ 925
Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Investments in equity method unconsolidated affiliates	$ 1,060	919
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	$ 25	81
Sabal Trail Transmission Pipeline [Member]
Variable Interest Entity [Line Items]
Investments in equity method unconsolidated affiliates	$ 112
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		219
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%
Investments in equity method unconsolidated affiliates	$ 797	397
Pipeline Investments [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Investments in equity method unconsolidated affiliates	822	697
Gas Utilities and Infrastructure [Member]
Variable Interest Entity [Line Items]
Investments in equity method unconsolidated affiliates	1,003	763	$ 566
Gas Utilities and Infrastructure [Member] | Constitution Pipeline [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
OTTI impairment loss	55
Gas Utilities and Infrastructure [Member] | Sabal Trail Transmission Pipeline [Member]
Variable Interest Entity [Line Items]
Investments in equity method unconsolidated affiliates	$ 112	$ 219