Property, Plant and Equipment (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Oil and Gas Exploration and Production Industries Disclosures [Abstract]
Total property, plant and equipment, net	$ 9,124		$ 9,124		$ 8,728
Unproved Oil and Natural Gas Properties
Property, plant, and equipment associated with unproven oil and natural gas properties	500		500		$ 700
Transfer from unproved properties to proved properties			200
Amortization of unproved leasehold costs	1	$ 4	$ 9	$ 15
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Projected inflation rate (as a percent)			2.50%
Changes in net asset retirement liability
Net asset retirement liability at January 1			$ 42
Liabilities incurred			4
Liabilities settled			(2)
Accretion expense			2
Changes in Estimate			(6)
Net asset retirement liability at September 30, 2015	40		40
Capitalized Interest
Capitalized interest	3	$ 6	$ 12	$ 16
Minimum
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Credit-adjusted risk-free rate (as a percent)			7.00%
Maximum
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Credit-adjusted risk-free rate (as a percent)			9.00%
Altamont [Member]
Unproved Oil and Natural Gas Properties
Property, plant, and equipment associated with unproven oil and natural gas properties	100		$ 100
Capitalized Costs, Oil and Gas Producing Activities, Net	1,000		1,000
Eagle Ford [Member]
Unproved Oil and Natural Gas Properties
Capitalized Costs, Oil and Gas Producing Activities, Net	5,000		5,000
Wolfcamp [Member]
Unproved Oil and Natural Gas Properties
Property, plant, and equipment associated with unproven oil and natural gas properties	400		400
Capitalized Costs, Oil and Gas Producing Activities, Net	$ 2,000		$ 2,000