Financial Risk Management - Corporate Financial Risk Management Activities - Additional Information (Detail)	3 Months Ended			6 Months Ended
	Jun. 30, 2015 USD ($) $ / bbl	Mar. 31, 2015 USD ($)	Jun. 30, 2014 USD ($)	Jun. 30, 2015 USD ($) BOPD $ / bbl	Jun. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)
Derivative [Line Items]
Floor price per barrel | $ / bbl	60			60
Ceiling price per barrel | $ / bbl	80			80
Interest Rate Swaps and Fixed-rate Debt [Member]
Derivative [Line Items]
Change in the fair value of interest rate swaps - increase/(decrease)	$ (6,000,000)		$ 4,000,000	$ 4,000,000	$ 5,000,000
Corporate Risk Management [Member] | Brent and West Texas Intermediate Crude Hedges [Member]
Derivative [Line Items]
Decrease in sales and other operating revenues as a result of losses from hedge	35,000,000		(10,000,000)	18,000,000	(1,000,000)
Gain (loss) on price risk fair value hedge ineffectiveness			(3,000,000)		(4,000,000)
Gain (loss) on fair value hedges recognized in earnings	(35,000,000)			(23,000,000)
After-tax deferred gains in Accumulated other comprehensive income (loss)	1,000,000			$ 1,000,000
Brent collars run from March 2015 to 12/31/15
Derivative [Line Items]
Total number of barrels per day hedged based on crude oil fixed-price swap contracts | BOPD				50,000
Cost of hedging				$ 38,000,000
WTI collars run from May 6 2015 to 12/31/15
Derivative [Line Items]
Total number of barrels per day hedged based on crude oil fixed-price swap contracts | BOPD				20,000
Cost of hedging				$ 10,000,000
Interest rate swap [Member]
Derivative [Line Items]
Derivative notional amount	1,300,000,000			1,300,000,000		$ 1,300,000,000
Derivative cash proceeds on hedge		$ 41,000,000
Foreign Exchange [Member]
Derivative [Line Items]
Gain (loss) on derivative instruments	(7,000,000)		(19,000,000)	8,000,000	(25,000,000)
Foreign Exchange [Member] | Not Designated Hedges [Member]
Derivative [Line Items]
Gain (loss) on derivative instruments	$ (41,000,000)		$ (13,000,000)	$ 57,000,000	$ (13,000,000)