Equity-Method Investments (Detail) - Equity-Method Investments [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2007
Schedule of Equity Method Investments [Line Items]
Ownership interest of investee entities	95.00%
Carrying amount of notes payable to affiliates	$ 2,900			$ 2,900
Carrying amount of investments	$ 2,800
Applicable interest rate	1.51%	1.24%
Interest expense on the notes payable	$ 37	$ 36	$ 37
Equity (earnings) losses from investments in the investee entities	$ 15	$ (45)	$ (42)
Maximum [Member]
Schedule of Equity Method Investments [Line Items]
Debt-to-capital ratio covenant	0.67
Contributed Property to Investees [Member]
Schedule of Equity Method Investments [Line Items]
Fair value of oil and gas properties and gathering and processing assets contributed by Anadarko				$ 2,900