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General, Description of Business, and Basis of Presentation (Details) - USD ($) $ / shares in Units, $ in Millions		1 Months Ended		3 Months Ended		6 Months Ended
	Jan. 09, 2017	Feb. 03, 2017	Jan. 31, 2017	Mar. 31, 2018	Mar. 31, 2017	Jun. 30, 2017	Jan. 01, 2018
Schedule of Equity Method Investments [Line Items]
Number Of Interstate Natural Gas Pipelines				2
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Operating Costs and Expenses				$ 357	$ 371
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Changes, Net				(2)
Other Nonoperating Income (Expense)				21	77
Operating Income (Loss)				(491)	(430)
Net Cash Provided by (Used in) Operating Activities				694	727
Net Cash Provided by (Used in) Investing Activities				$ 798	243
Constitution Pipeline Company LLC [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Variable Interest Entity Ownership Percentage				41.00%
Appalachia Midstream Services, LLC [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Subsidiary of Limited Liability Company or Limited Partnership, Ownership Interest				66.00%
Noncontrolling Interest [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Changes, Net				$ (9)
Capital in excess of par value [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Changes, Net				$ 7
Limited Partner [Member] \| Williams Partners L.P. [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Variable Interest Entity Ownership Percentage				74.00%
Financial Repositioning [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Sale of Stock, Number of Shares Issued in Transaction	277,000	59,000,000	289,000,000
Payments to Acquire Limited Partnership Interests	$ 10					$ 56
Sale of Stock, Price Per Share		$ 36.08586
Financial Repositioning [Member] \| Williams Partners L.P. [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Limited Liability Company (LLC) or Limited Partnership (LP), Managing Member or General Partner, Ownership Interest			2.00%
Williams Partners [Member] \| Dividend Reinvestment Program [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Sale of Stock, Number of Shares Issued in Transaction				576,923
Sale of Stock, Consideration Received on Transaction				$ 22
Accounting Standards Update 201707 [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Operating Costs and Expenses					3
Other Nonoperating Income (Expense)					3
Operating Income (Loss)					3
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							$ 121
Gulfstream Natural Gas System, L.L.C.[Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage				50.00%
Utica East Ohio Midstream, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage				62.00%
Delaware Basin Gas Gathering System [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage					50.00%
Delaware Basin Gas Gathering System [Member] \| Williams Partners [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage					50.00%
Laurel Mountain Midstream, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage				69.00%
Caiman Energy II [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage				58.00%
Discovery Producer Services LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage				60.00%
Overland Pass Pipeline Company LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage				50.00%
Reclassification out of Accumulated Other Comprehensive Income [Member] \| Accounting Standards Update 2018-02 [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							61
Retained Deficit \| Accounting Standards Update 2018-02 [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							$ (61)