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Total units issued during the year due to the sale of units. All partners include general, limited and preferred partners.

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General, Description of Business, and Basis of Presentation (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions		1 Months Ended		3 Months Ended		6 Months Ended	9 Months Ended
	Jan. 09, 2017	Feb. 03, 2017	Jan. 31, 2017	Mar. 31, 2018	Mar. 31, 2017	Jun. 30, 2017	Sep. 30, 2017	Jan. 01, 2018
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Net Cash Provided by (Used in) Operating Activities				$ 752	$ 852
Proceeds from sales of common units				0	2,178
Net Cash Provided by (Used in) Investing Activities				$ 789	$ 238
The Williams Companies, Inc. [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Parent, limited partner ownership percentage				74.00%
Financial Repositioning [Member] \| The Williams Companies, Inc. [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Parent, general partner ownership percentage			2.00%
Partners' Capital Account, Units, Sale of Units	277		289,000
Proceeds from sales of common units	$ 10					$ 56
Partners' Capital Account, Units, Sold in Private Placement		59,000
Shares Issued, Price Per Share		$ 36.08586
Delaware Basin Gas Gathering System [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage					50.00%
Northeast G And P [Member] \| Cardinal Gas Services LLC [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Variable Interest Entity Ownership Percentage				66.00%
Northeast G And P [Member] \| Appalachia Midstream Services, LLC [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Subsidiary, ownership percentage				66.00%
Northeast G And P [Member] \| Utica East Ohio Midstream, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage				62.00%
Northeast G And P [Member] \| Laurel Mountain Midstream, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage				69.00%
Northeast G And P [Member] \| Caiman Energy II, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage				58.00%
Atlantic Gulf [Member] \| Gulfstar One [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Variable Interest Entity Ownership Percentage				51.00%
Atlantic Gulf [Member] \| Constitution Pipeline Company LLC [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Variable Interest Entity Ownership Percentage				41.00%
Atlantic Gulf [Member] \| Gulfstream Natural Gas System, L.L.C. [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage				50.00%
Atlantic Gulf [Member] \| Discovery Producer Services LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage				60.00%
NGL And Petchem Services [Member] \| Geismar [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Subsidiary, ownership percentage							88.50%
West [Member] \| Conway Fractionator [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Subsidiary, ownership percentage				50.00%
West [Member] \| Delaware Basin Gas Gathering System [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage					50.00%
West [Member] \| Overland Pass Pipeline Company LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage				50.00%
Accounting Standards Update 2016-15 [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Net Cash Provided by (Used in) Operating Activities					$ 121
Net Cash Provided by (Used in) Investing Activities					$ 121
Accounting Standards Update 2014-09 [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets								$ 148