Fair Value Measurements Nonrecurring Measurements (Details) - USD ($) $ in Millions		3 Months Ended					6 Months Ended
		Jun. 30, 2019		Mar. 31, 2019		Jun. 30, 2018	Jun. 30, 2019		Jun. 30, 2018	Mar. 17, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Tangible Asset Impairment Charges							$ 76		$ 66
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Impairment of equity-method investments (Note 5)		$ (2)				$ 0	72		0
Impairment Of Certain Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Tangible Asset Impairment Charges							76		66
Fair Value, Measurements, Nonrecurring [Member] | Impairment Of Certain Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Tangible Asset Impairment Charges							5		0
Fair Value, Measurements, Nonrecurring [Member] | Level 3 [Member] | Investments [Member] | Northeast G And P [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value Disclosure	[1]									$ 1,209
Fair Value, Measurements, 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	[2]	$ 0	[3]		40	[2]
Fair Value, Measurements, Nonrecurring [Member] | Level 3 [Member] | Impairment Of Certain Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Tangible Asset Impairment Charges							$ 71
Fair Value, Measurements, Nonrecurring [Member] | Level 3 [Member] | Impairment Of Certain Assets [Member] | West [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Tangible Asset Impairment Charges		59	[2]	12	[3]
Fair Value, Measurements, Nonrecurring [Member] | Level 3 [Member] | Impairment Of Equity-Method Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Impairment of equity-method investments (Note 5)		$ (2)
Fair Value, Measurements, 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]
Impairment of equity-method investments (Note 5)	[1]			$ 74
Fair Value, Measurements, Nonrecurring [Member] | Level 2 [Member] | Property Plant And Equipment, net [Member] | Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Fair Value of Property, Plant, and Equipment	[4]					25			25
Fair Value, Measurements, Nonrecurring [Member] | Level 2 [Member] | Impairment Of Certain Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Tangible Asset Impairment Charges									$ 66
Fair Value, Measurements, Nonrecurring [Member] | Level 2 [Member] | Impairment Of Certain Assets [Member] | Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Tangible Asset Impairment Charges	[4]					$ 66

[1] Relates to Northeast G&P’s equity-method investment in UEOM. 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). This impairment is reported in Other investing income (loss) - net in the Consolidated Statement of Income.

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

[3] Reflects impairment of assets that are no longer in use for which the fair value was determined to be lower than the carrying value.

[4] Relates to certain idle pipelines. The estimated fair value was determined by a market approach incorporating information derived from bids received for these assets, which we marketed for sale together with certain other assets. These inputs resulted in a fair value measurement within Level 2 of the fair value hierarchy. We sold these assets in the fourth quarter of 2018.