Debt - Additional Information (Detail) - USD ($)	6 Months Ended
	Jun. 30, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Total borrowings at face value	$ 16,839,000,000	$ 16,706,000,000
APC RCF [Member]
Debt Instrument [Line Items]
Line of credit, maximum capacity	$ 3,000,000,000
Line of credit, expiration date	Jan. 23, 2021
Line of credit, outstanding borrowings	$ 0
364-Day Credit Facility Due 2017 [Member]
Debt Instrument [Line Items]
Line of credit, maximum capacity	$ 2,000,000,000
Debt instrument, term	364 days
Line of credit, expiration date	Jan. 12, 2018
Line of credit, outstanding borrowings	$ 0
WES RCF [Member]
Debt Instrument [Line Items]
Line of credit, maximum capacity	$ 1,200,000,000
Line of credit, expiration date	Feb. 26, 2020
Line of credit, outstanding borrowings	$ 160,000,000
Line of credit, interest rate	2.53%
Line of credit, expandable maximum capacity	$ 1,500,000,000
Borrowings during period	160,000,000
Letters of credit, outstanding	5,000,000
Line of credit, available borrowing capacity	1,035,000,000
WGP RCF [Member]
Debt Instrument [Line Items]
Line of credit, maximum capacity	$ 250,000,000
Debt instrument, term	3 years
Line of credit, expiration date	Mar. 14, 2019
Line of credit, outstanding borrowings	$ 28,000,000
Line of credit, interest rate	3.23%
Line of credit, expandable maximum capacity	$ 500,000,000
Line of credit, available borrowing capacity	222,000,000
Fair Value, Inputs, Level 2 [Member] | Market Approach Valuation Technique [Member]
Debt Instrument [Line Items]
Estimated fair value of total borrowings	17,200,000,000	$ 17,100,000,000
7.050% Debentures due 2018
Debt Instrument [Line Items]
Total borrowings at face value	$ 114,000,000
Line of credit, interest rate	7.05%
Zero-Coupon Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, earliest call date	Oct. 10, 2017
Zero-Coupon Senior Notes [Member] | Accreted Value at Next Potential Put Date [Member]
Debt Instrument [Line Items]
Debt instrument, accreted value	$ 883,000,000