Investing Activities (Details) - USD ($) $ in Millions				3 Months Ended		12 Months Ended
		Nov. 18, 2020	Dec. 31, 2019	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 15, 2018
Schedule of Investments [Line Items]
Income (Loss) from Equity Method Investments						$ (328)	$ (375)	$ (396)
Impairment of equity-method investments (Note 18)						(1,046)	(186)	(32)
Deconsolidation, Revaluation of Retained Investment, Gain (Loss), Amount						0	(29)	203
Gain on disposition of equity-method investment						0	122	0
Other investing income (loss) - net						8	107	219
Equity-method investment, payments to purchase or contributions						325	453	1,132
Equity-method investments			$ 6,235			5,159	6,235
Proceeds from dispositions of equity-method investments						0	485	0
Equity-method investment, difference between carrying amount and underlying equity			360			1,300	360
Distributions from unconsolidated affiliates						653	657	693
Current assets			1,580			1,429	1,580
Current liabilities			(3,968)			(2,319)	(3,968)
Revenues						7,719	8,201	8,686
Operating income						508	685	804
Net income						198	714	193
Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member]
Schedule of Investments [Line Items]
Current assets			581			630	581
Noncurrent assets			11,966			13,424	11,966
Current liabilities			(341)			(312)	(341)
Noncurrent liabilities			(2,532)			(3,884)	(2,532)
Revenues						2,625	2,490	2,411
Net income						459	598	$ 795
Measurement Input, Discount Rate [Member]
Schedule of Investments [Line Items]
Property Plant And Equipment And Intangibles Fair Value Inputs								8.50%
Other Income [Member]
Schedule of Investments [Line Items]
Other investing income (loss) - net						$ 8	14	$ 16
Appalachia Midstream Investments [Member]
Schedule of Investments [Line Items]
Equity Method Investment, Ownership Percentage						66.00%
Income (Loss) from Equity Method Investments						$ 26
Equity-method investment, payments to purchase or contributions						116	140	246
Equity-method investments	[1]		3,236			3,087	3,236
Equity-method investment, difference between carrying amount and underlying equity			1,400			1,200	1,400
Distributions from unconsolidated affiliates						$ 357	293	297
Rocky Mountain Midstream Holdings LLC [Member]
Schedule of Investments [Line Items]
Equity Method Investment, Ownership Percentage						50.00%
Income (Loss) from Equity Method Investments						$ 78
Equity-method investment, payments to purchase or contributions						0	145	795
Equity-method investments			881			421	881
Distributions from unconsolidated affiliates						$ 39	38	0
Discovery Producer Services LLC [Member]
Schedule of Investments [Line Items]
Equity Method Investment, Ownership Percentage						60.00%
Equity-method investment, payments to purchase or contributions						$ 0	0	5
Equity-method investments			472			352	472
Distributions from unconsolidated affiliates						$ 21	41	45
Caiman Energy II [Member]
Schedule of Investments [Line Items]
Equity-method investment, payments to purchase or contributions							28	0
Equity-method investments			428				428
Distributions from unconsolidated affiliates							42	46
Overland Pass Pipeline Company LLC [Member]
Schedule of Investments [Line Items]
Equity Method Investment, Ownership Percentage						50.00%
Equity-method investments			403			$ 395	403
Distributions from unconsolidated affiliates						$ 50	77	73
Laurel Mountain Midstream, LLC [Member]
Schedule of Investments [Line Items]
Equity Method Investment, Ownership Percentage						69.00%
Income (Loss) from Equity Method Investments						$ 11
Equity-method investment, payments to purchase or contributions						5	36	16
Equity-method investments			249			219	249
Distributions from unconsolidated affiliates						$ 31	30	23
Gulfstream Natural Gas System, LLC [Member]
Schedule of Investments [Line Items]
Equity Method Investment, Ownership Percentage						50.00%
Equity-method investments			217			$ 204	217
Distributions from unconsolidated affiliates						$ 93	86	$ 93
Brazos Permian II, LLC [Member]
Schedule of Investments [Line Items]
Equity Method Investment, Ownership Percentage						15.00%		15.00%
Equity-method investment, payments to purchase or contributions						$ 0	18	$ 27
Equity-method investments			194			0	194
Utica East Ohio Midstream, LLC [Member]
Schedule of Investments [Line Items]
Equity Method Investment, Ownership Percentage								62.00%
Distributions from unconsolidated affiliates						0	13	$ 70
Jackalope Gas Gathering Services LLC [Member]
Schedule of Investments [Line Items]
Equity Method Investment, Ownership Percentage				50.00%	50.00%
Gain on disposition of equity-method investment				$ 122
Equity-method investment, payments to purchase or contributions						0	24	42
Proceeds from dispositions of equity-method investments				$ 485
Constitution Pipeline Company LLC [Member]
Schedule of Investments [Line Items]
Deconsolidation, Revaluation of Retained Investment, Gain (Loss), Amount							27
Other [Member]
Schedule of Investments [Line Items]
Equity-method investment, payments to purchase or contributions						41	19	1
Equity-method investments			$ 155			124	155
Distributions from unconsolidated affiliates						15	37	46
Total Equity Method Investment [Member]
Schedule of Investments [Line Items]
Distributions from unconsolidated affiliates						653	657	693
Targa Train 7 LLC [Member]
Schedule of Investments [Line Items]
Equity-method investment, payments to purchase or contributions						$ 6	$ 43	0
Blue Racer Midstream LLC [Member]
Schedule of Investments [Line Items]
Equity Method Investment, Ownership Percentage						50.00%
Income (Loss) from Equity Method Investments						$ 10
Equity-method investment, payments to purchase or contributions		$ 157				157
Equity-method investments						357
Distributions from unconsolidated affiliates						$ 47
Northeast G And P [Member] | Caiman Energy II [Member]
Schedule of Investments [Line Items]
Equity Method Investment, Ownership Percentage			58.00%				58.00%
Northeast G And P [Member] | Laurel Mountain Midstream, LLC [Member]
Schedule of Investments [Line Items]
Equity Method Investment, Ownership Percentage						69.00%
Northeast G And P [Member] | Blue Racer Midstream LLC [Member]
Schedule of Investments [Line Items]
Equity Method Investment, Ownership Percentage						50.00%
West [Member] | Rocky Mountain Midstream Holdings LLC [Member]
Schedule of Investments [Line Items]
Equity Method Investment, Ownership Percentage						50.00%
West [Member] | Overland Pass Pipeline Company LLC [Member]
Schedule of Investments [Line Items]
Equity Method Investment, Ownership Percentage						50.00%
West [Member] | Brazos Permian II, LLC [Member]
Schedule of Investments [Line Items]
Deconsolidation, Revaluation of Retained Investment, Gain (Loss), Amount								$ 141
West [Member] | Jackalope Gas Gathering Services LLC [Member]
Schedule of Investments [Line Items]
Deconsolidation, Revaluation of Retained Investment, Gain (Loss), Amount					$ 62
Goodwill, Period Increase (Decrease)					47
West [Member] | Targa Train 7 LLC [Member]
Schedule of Investments [Line Items]
Equity Method Investment, Ownership Percentage						20.00%
Caiman Energy II Acquisition [Member] | Caiman Energy II [Member]
Schedule of Investments [Line Items]
Business Acquisition, Percentage of Voting Interests Acquired		41.00%
Brazos Permian II, LLC [Member] | West [Member]
Schedule of Investments [Line Items]
Investments, Fair Value Disclosure									$ 192
Jackalope Gas Gathering Services LLC [Member] | West [Member]
Schedule of Investments [Line Items]
Investments, Fair Value Disclosure					$ 310
Jackalope Gas Gathering Services LLC [Member] | West [Member] | Measurement Input, Discount Rate [Member]
Schedule of Investments [Line Items]
Property Plant And Equipment And Intangibles Fair Value Inputs					10.90%
Caiman Energy II [Member] | Blue Racer Midstream LLC [Member]
Schedule of Investments [Line Items]
Limited Liability Company or Limited Partnership, Members or Limited Partners, Ownership Interest			50.00%
Beneficial Owner [Member] | Williams Companies Inc [Member] | Blue Racer Midstream LLC [Member]
Schedule of Investments [Line Items]
Limited Liability Company or Limited Partnership, Members or Limited Partners, Ownership Interest			29.00%

[1] Includes equity-method investments in multiple gathering systems in the Marcellus Shale with an approximate average 66 percent interest.(2)See previous discussion in the section Acquisition of Additional Interests in Caiman II above.