Summary of Significant Accounting Policies - Additional Information (Detail) $ / shares in Units, $ in Millions			3 Months Ended		6 Months Ended
	May 09, 2019 $ / shares shares	Feb. 28, 2019 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) Segment	Jun. 30, 2018 USD ($)	Apr. 11, 2019 USD ($)	Jan. 01, 2019 USD ($)		Jan. 01, 2018 USD ($)	[2]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Merger transaction costs			$ 1,042	$ 0	$ 1,042	$ 0
Sale of assets, consideration		$ 4,000
Cash proceeds from sale of assets		2,000
Number of reporting segments | Segment					2
Cumulative effect of accounting change								$ (55)	[1]	$ (47)
ASU 2016-02 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
ROU Assets								600
Lease liabilities								600
Cumulative effect of accounting change								$ 55
WES Operating [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Common units received from sale of assets		$ 2,000
WES Operating [Member] | Limited Partner [Member] | WES [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Ownership interest in subsidiary		98.00%
WES Operating [Member] | Limited Partner [Member] | Anadarko Limited Partner Interest In WES [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Ownership interest in subsidiary		2.00%	2.00%		2.00%
WES [Member] | Limited Partner [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Ownership interest in subsidiary		55.50%
WES [Member] | Limited Partner [Member] | Anadarko Limited Partner Interest In WES [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Ownership interest in subsidiary			55.50%		55.50%
Anadarko, Chevron offer [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Merger, termination fee							$ 1,000
Anadarko [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Business Acquisition, Transaction Costs			$ 42		$ 42
Anadarko [Member] | Occidental [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Merger, cash received per share (in usd per share) | $ / shares	$ 59.00
Merger, shares received (in shares) | shares	0.2934

[1] Beginning January 1, 2019, the Company adopted ASU 2016-02, Leases (Topic 842). See Note 1—Summary of Significant Accounting Policies in the Notes to Consolidated Financial Statements for further information.

[2] Beginning January 1, 2018, the Company adopted ASU 2014-09, Revenue from Contracts with Customers (Topic 606), and ASU 2018-02, Income Statement - Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income. See Note 1—Summary of Significant Accounting Policies in the Company’s Annual Report on Form 10-K for the year ended December 31, 2018.