Variable Interest Entities (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
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	$ 26	$ 33
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	50	62
Variable Interest Entity, Primary Beneficiary [Member] | Other Current Assets [Member]
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net [Abstract]
Variable Interest Entity, Consolidated, Carrying Amount, Assets	1	2
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	2,333	2,363
Variable Interest Entity, Primary Beneficiary [Member] | Intangible Assets, net [Member]
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net [Abstract]
Variable Interest Entity, Consolidated, Carrying Amount, Assets	1,166	1,177
Variable Interest Entity, Primary Beneficiary [Member] | Regulatory assets, Deferred Charges, and Other Noncurrent Assets [Member]
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net [Abstract]
Variable Interest Entity, Consolidated, Carrying Amount, Assets	1	0
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)	(15)
Variable Interest Entity, Primary Beneficiary [Member] | Accrued Liabilities including current asset retirement obligations [Member]
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net [Abstract]
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities	(115)	(115)
Variable Interest Entity, Primary Beneficiary [Member] | Noncurrent Asset Retirement Obligation [Member]
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net [Abstract]
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities	(107)	(105)
Variable Interest Entity, Primary Beneficiary [Member] | Other Noncurrent Liabilities [Member]
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net [Abstract]
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities	$ (137)	$ (159)
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, 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, Not Primary Beneficiary [Member] | Jackalope Gas Gathering Services LLC [Member] | Investments [Domain]
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net [Abstract]
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets and Liabilities, Net	$ 358
Variable Interest Entity, Not Primary Beneficiary [Member] | Brazos Permian II LLC [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity Ownership Percentage	15.00%
Variable Interest Entity, Not Primary Beneficiary [Member] | Brazos Permian II LLC [Member] | Investments [Domain]
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net [Abstract]
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets and Liabilities, Net	$ 190