Fair Value Measurements and Guarantees Nonrecurring Measurements (Details) - USD ($) $ in Millions												1 Months Ended		3 Months Ended					9 Months Ended
		Mar. 31, 2020		Sep. 30, 2019		Aug. 31, 2019	Jun. 30, 2019	[1]	Mar. 31, 2019	[2]	Mar. 17, 2019	Mar. 31, 2020		Sep. 30, 2020	Mar. 31, 2020		Sep. 30, 2019		Sep. 30, 2020	Sep. 30, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Share Price Change												26.00%			40.00%
Goodwill, Impairment Loss														$ 0			$ 0		$ 187	$ 0
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Tangible Asset Impairment Charges																			0	76
Equity Method Investment, Other than Temporary Impairment														$ 0			114		938	186
Impairment Of Certain Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Tangible Asset Impairment Charges																				76
Impairment Of Equity-Method Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Equity Method Investment, Other than Temporary Impairment																			938	186
Fair Value, Nonrecurring [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Goodwill, Impairment Loss															$ 187
Fair Value, Nonrecurring [Member] | Level 3 [Member] | Property, Plant, and Equipment, net [Member] | West [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Fair Value of Property, Plant, and Equipment							$ 40		$ 0
Fair Value, Nonrecurring [Member] | Level 3 [Member] | Impairment Of Certain Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Tangible Asset Impairment Charges																				5
Fair Value, Nonrecurring [Member] | Level 3 [Member] | Impairment Of Certain Assets [Member] | West [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Tangible Asset Impairment Charges							$ 59		$ 12
Fair Value, Nonrecurring [Member] | Level 3 [Member] | Impairment Of Equity-Method Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Equity Method Investment, Other than Temporary Impairment																			$ 0	(1)
Williams Companies Inc [Member] | Appalachia Midstream Services, LLC [Member] | Fair Value, Nonrecurring [Member] | Level 3 [Member] | Investments [Member] | Northeast G And P [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Investments, Fair Value Disclosure		$ 2,700	[3]	$ 102	[4]							$ 2,700	[3]		2,700	[3]	$ 102	[4]		$ 102	[4]
Williams Companies Inc [Member] | Appalachia Midstream Services, LLC [Member] | Fair Value, Nonrecurring [Member] | Level 3 [Member] | Impairment Of Equity-Method Investments [Member] | Northeast G And P [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Equity Method Investment, Other than Temporary Impairment		127	[3]	$ 17	[4]
Rocky Mountain Midstream Holdings LLC [Member] | Fair Value, Nonrecurring [Member] | Level 3 [Member] | Investments [Member] | West [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Investments, Fair Value Disclosure	[5]	557										$ 557			$ 557
Rocky Mountain Midstream Holdings LLC [Member] | Fair Value, Nonrecurring [Member] | Level 3 [Member] | Impairment Of Equity-Method Investments [Member] | West [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Equity Method Investment, Other than Temporary Impairment	[5]	$ 243
Rocky Mountain Midstream Holdings LLC [Member] | Measurement Input, Discount Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Investments Fair Value Inputs		17.00%										17.00%			17.00%
Brazos Permian II LLC [Member] | Fair Value, Nonrecurring [Member] | Level 3 [Member] | Investments [Member] | West [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Investments, Fair Value Disclosure	[5]	$ 0										$ 0			$ 0
Brazos Permian II LLC [Member] | Fair Value, Nonrecurring [Member] | Level 3 [Member] | Impairment Of Equity-Method Investments [Member] | West [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Equity Method Investment, Other than Temporary Impairment	[5]	$ 193
Brazos Permian II LLC [Member] | Measurement Input, Discount Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Investments Fair Value Inputs		17.00%										17.00%			17.00%
Caiman Energy II [Member] | Fair Value, Nonrecurring [Member] | Level 3 [Member] | Investments [Member] | Northeast G And P [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Investments, Fair Value Disclosure	[3]	$ 191										$ 191			$ 191
Caiman Energy II [Member] | Fair Value, Nonrecurring [Member] | Level 3 [Member] | Impairment Of Equity-Method Investments [Member] | Northeast G And P [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Equity Method Investment, Other than Temporary Impairment	[3]	229
Appalachia Midstream Services, LLC [Member] | Measurement Input, Discount Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Investments Fair Value Inputs				9.00%													9.00%			9.00%
Aux Sable Liquid Products LP [Member] | Fair Value, Nonrecurring [Member] | Level 3 [Member] | Investments [Member] | Northeast G And P [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Investments, Fair Value Disclosure	[3]	7										7			7
Aux Sable Liquid Products LP [Member] | Fair Value, Nonrecurring [Member] | Level 3 [Member] | Impairment Of Equity-Method Investments [Member] | Northeast G And P [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Equity Method Investment, Other than Temporary Impairment	[3]	39
Laurel Mountain Midstream, LLC [Member] | Fair Value, Nonrecurring [Member] | Level 3 [Member] | Investments [Member] | Northeast G And P [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Investments, Fair Value Disclosure		236	[3]	$ 242	[6]							236	[3]		236	[3]	$ 242	[6]		$ 242	[6]
Laurel Mountain Midstream, LLC [Member] | Fair Value, Nonrecurring [Member] | Level 3 [Member] | Impairment Of Equity-Method Investments [Member] | Northeast G And P [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Equity Method Investment, Other than Temporary Impairment		10	[3]	$ 79	[6]
Laurel Mountain Midstream, LLC [Member] | Measurement Input, Discount Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Investments Fair Value Inputs				10.20%													10.20%			10.20%
Discovery Producer Services LLC [Member] | Fair Value, Nonrecurring [Member] | Level 3 [Member] | Investments [Member] | Transmission And Gulf Of Mexico [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Investments, Fair Value Disclosure	[3]	367										$ 367			$ 367
Discovery Producer Services LLC [Member] | Fair Value, Nonrecurring [Member] | Level 3 [Member] | Impairment Of Equity-Method Investments [Member] | Transmission And Gulf Of Mexico [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Equity Method Investment, Other than Temporary Impairment	[3]	$ 97
Pennant Midstream, LLC (Member) | Fair Value, Nonrecurring [Member] | Level 2 [Member] | Investments [Member] | Northeast G And P [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Investments, Fair Value Disclosure	[7]					$ 11
Pennant Midstream, LLC (Member) | Fair Value, Nonrecurring [Member] | Level 2 [Member] | Impairment Of Equity-Method Investments [Member] | Northeast G And P [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Equity Method Investment, Other than Temporary Impairment	[7]					$ 17
Utica East Ohio Midstream, LLC [Member] | Fair Value, Nonrecurring [Member] | Level 2 [Member] | Investments [Member] | Northeast G And P [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Investments, Fair Value Disclosure	[8]										$ 1,210
Utica East Ohio Midstream, LLC [Member] | Fair Value, Nonrecurring [Member] | Level 2 [Member] | Impairment Of Equity-Method Investments [Member] | Northeast G And P [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Equity Method Investment, Other than Temporary Impairment	[8]										$ 74
Minimum [Member] | Caiman Energy II And Aux Sable Liquid Products LP [Member] | Measurement Input, EBITDA Multiple [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Investments Fair Value Inputs		500.00%										500.00%			500.00%
Minimum [Member] | Appalachia Midstream Services LLC And Laurel Mountain Midstream LLC And Discovery Producer Services LLC [Member] | Measurement Input, Discount Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Investments Fair Value Inputs		9.70%										9.70%			9.70%
Maximum [Member] | Caiman Energy II And Aux Sable Liquid Products LP [Member] | Measurement Input, EBITDA Multiple [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Investments Fair Value Inputs		620.00%										620.00%			620.00%
Maximum [Member] | Appalachia Midstream Services LLC And Laurel Mountain Midstream LLC And Discovery Producer Services LLC [Member] | Measurement Input, Discount Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Investments Fair Value Inputs		13.50%										13.50%			13.50%
Weighted Average [Member] | Caiman Energy II And Aux Sable Liquid Products LP [Member] | Measurement Input, EBITDA Multiple [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Investments Fair Value Inputs		600.00%										600.00%			600.00%
Weighted Average [Member] | Appalachia Midstream Services LLC And Laurel Mountain Midstream LLC And Discovery Producer Services LLC [Member] | Measurement Input, Discount Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Investments Fair Value Inputs		12.60%										12.60%			12.60%
Noncontrolling Interests
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Goodwill, Impairment Loss															$ 65

[1] Relates to a gas gathering system in the Eagle Ford Shale region with expected declines in asset utilization and possible idling of the gathering system. The estimated fair value of the Property, plant, and equipment – net was determined using a market approach which incorporated indications of interest from third parties.

[2] Reflects impairment of Property, plant, and equipment – net that is no longer in use for which the fair value was determined to be lower than the carrying value.

[3] Following the previously described declining market conditions during the first quarter of 2020, we evaluated these investments for other-than-temporary impairment. The impairments within our Northeast G&P segment are primarily associated with operations in wet-gas areas where producer drilling activities are influenced by NGL prices which historically trend with crude oil prices. The fair values of our investments in Caiman II and Aux Sable Liquid Products LP (Aux Sable) were estimated using a market approach, reflecting valuation multiples ranging from 5.0x to 6.2x EBITDA (weighted-average 6.0x). The fair values of the other investments, including gathering systems that are part of Appalachia Midstream Investments, were estimated using an income approach, with discount rates ranging from 9.7 percent to 13.5 percent (weighted-average 12.6 percent). We also considered any debt held at the investee level, and its impact to fair value. The assumed valuation multiples and industry weighted-average discount rates utilized were both significantly influenced by the recent market declines previously discussed.

[4] Relates to a certain gathering system held in Appalachia Midstream Investments that was adversely impacted by changes in the timing of expected producer activity. The estimated fair value was determined using an income approach. We utilized a discount rate of 9.0 percent in our analysis.

[5] Following the previously described declining market conditions during the first quarter of 2020, we evaluated these investments for other-than-temporary impairment. The fair value was measured using an income approach. Both investees operate in primarily oil-driven basins where significant expected reductions in producer activities led to reduced estimates of expected future cash flows. Our fair value estimates also reflected discount rates of approximately 17 percent for these investments. We also considered any debt held at the investee level, and its impact to fair value. The industry weighted-average discount rates utilized were significantly influenced by the recent market declines previously discussed.

[6] Relates to a gas gathering system in the Marcellus region that was adversely impacted by lower sustained forward natural gas price expectations and changes in expected producer activity. The estimated fair value was determined using an income approach. We utilized a discount rate of 10.2 percent in our analysis.

[7] The estimated fair value of Pennant Midstream, LLC (Pennant) was determined by a market approach based on recent observable third-party transactions. These inputs resulted in a fair value measurement within Level 2 of the fair value hierarchy.

[8] The estimated fair value was determined by a market approach based on the transaction price for the purchase of the remaining interest in UEOM as finalized just prior to the signing and closing of the acquisition in March 2019 (see Note 2 – Acquisitions). These inputs resulted in a fair value measurement within Level 2 of the fair value hierarchy.