Variable Interest Entities (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Dec. 31, 2017	[1]
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	$ 32	$ 881
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	57	972
Variable Interest Entity, Primary Beneficiary [Member] | Inventories [Member]
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net [Abstract]
Variable Interest Entity, Consolidated, Carrying Amount, Assets	0	113
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	176
Variable Interest Entity, Primary Beneficiary [Member] | Investments [Member]
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net [Abstract]
Variable Interest Entity, Consolidated, Carrying Amount, Assets	0	6,552
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	2,398	27,912
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	1,189	8,790
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	0	507
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	(16)	(957)
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	(98)	(857)
Variable Interest Entity, Primary Beneficiary [Member] | Long-term debt due within one year [Member]
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net [Abstract]
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities	0	(501)
Variable Interest Entity, Primary Beneficiary [Member] | Long-term Debt [Member]
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net [Abstract]
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities	0	(15,996)
Variable Interest Entity, Primary Beneficiary [Member] | Deferred Income Tax Liabilities [Member]
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net [Abstract]
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities	0	(16)
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	(104)	(944)
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	$ (189)	$ (2,809)
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	$ 377
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] | Estimated Remaining Construction Costs For Variable Interest Entity [Member]
Variable Interest Entity [Line Items]
Other commitment	$ 400
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	$ 316

[1] Includes WPZ, which was a consolidated VIE at December 31, 2017 (see Note 1 – General, Description of Business, and Basis of Presentation).