Variable Interest Entities (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended	9 Months Ended
	Apr. 30, 2019	Dec. 31, 2018	Sep. 30, 2019	Sep. 30, 2018	Jun. 30, 2019
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net [Abstract]
Proceeds from Sale of Equity Method Investments			$ 485	$ 0
Northeast JV [Member]
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net [Abstract]
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners					35.00%
Jackalope Gas Gathering Services LLC [Member]
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net [Abstract]
Proceeds from Sale of Equity Method Investments	$ 485
Variable Interest Entity, Primary Beneficiary [Member] | Cash and cash equivalents [Member]
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net [Abstract]
Variable Interest Entity, Consolidated, Carrying Amount, Assets		$ 33	90
Variable Interest Entity, Primary Beneficiary [Member] | Trade accounts and other receivables - net [Member]
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net [Abstract]
Variable Interest Entity, Consolidated, Carrying Amount, Assets		62	152
Variable Interest Entity, Primary Beneficiary [Member] | Other current assets and deferred charges [Member]
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net [Abstract]
Variable Interest Entity, Consolidated, Carrying Amount, Assets		2	5
Variable Interest Entity, Primary Beneficiary [Member] | Property plant and equipment, net [Member]
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net [Abstract]
Variable Interest Entity, Consolidated, Carrying Amount, Assets		2,363	6,167
Variable Interest Entity, Primary Beneficiary [Member] | Intangible assets - net of accumulated amortization [Member]
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net [Abstract]
Variable Interest Entity, Consolidated, Carrying Amount, Assets		1,177	2,697
Variable Interest Entity, Primary Beneficiary [Member] | Regulatory assets, deferred charges, and other [Member]
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net [Abstract]
Variable Interest Entity, Consolidated, Carrying Amount, Assets		0	13
Variable Interest Entity, Primary Beneficiary [Member] | Accounts payable [Member]
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net [Abstract]
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities		(15)	(54)
Variable Interest Entity, Primary Beneficiary [Member] | Accrued liabilities [Member]
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net [Abstract]
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities		(115)	(100)
Variable Interest Entity, Primary Beneficiary [Member] | Regulatory liabilities, deferred income, and other [Member]
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net [Abstract]
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities		$ (264)	$ (268)
Variable Interest Entity, Primary Beneficiary [Member] | Gulfstar One [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity Ownership Percentage			51.00%
Variable Interest Entity, Primary Beneficiary [Member] | Constitution Pipeline Company LLC [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity Ownership Percentage			41.00%
Variable Interest Entity, Primary Beneficiary [Member] | Constitution Pipeline Company LLC [Member] | Estimated Remaining Construction Costs For Variable Interest Entity [Member]
Variable Interest Entity [Line Items]
Other commitment			$ 740
Variable Interest Entity, Primary Beneficiary [Member] | Constitution Pipeline Company LLC [Member] | Property plant and equipment, net [Member]
Variable Interest Entity [Line Items]
Capitalized Project Development Costs			$ 376
Variable Interest Entity, Primary Beneficiary [Member] | Cardinal Gas Services LLC [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity Ownership Percentage			66.00%
Variable Interest Entity, Primary Beneficiary [Member] | Northeast JV [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity Ownership Percentage			65.00%
Variable Interest Entity, Not Primary Beneficiary [Member] | Jackalope Gas Gathering Services LLC [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity Ownership Percentage		50.00%
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net [Abstract]
Proceeds from Sale of Equity Method Investments	$ 485
Variable Interest Entity, Not Primary Beneficiary [Member] | Brazos Permian II LLC [Member] | Investments [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity Ownership Percentage			15.00%
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net [Abstract]
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets and Liabilities, Net			$ 197