Basis of Presentation (Details) $ / shares in Units, $ in Millions					3 Months Ended		9 Months Ended		12 Months Ended
		Jul. 20, 2015 shares	Mar. 25, 2015 $ / shares shares	Mar. 03, 2015 $ / shares shares	Sep. 30, 2015 USD ($) $ / shares shares	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($) $ / shares shares	Sep. 30, 2014 USD ($)	Dec. 31, 2014 USD ($) $ / shares shares
Non-qualified defined benefit plans in AOCL							$ 16
Common stock, par value per share (in dollars per share) | $ / shares					$ 0.01		$ 0.01		$ 0.01
Proceeds from Issuance of Shares of Common Stock to Public, Net of Offering Costs							$ 1,112	$ 0
Repayment of outstanding indebtedness							$ 150
Common stock, shares authorized (in shares) | shares					1,000,000,000		1,000,000,000		500,000,000
Debt Issuance Cost							$ 49		$ 50
Shares exchange in acquisition | shares		41,000,000
Production Expense
Lease Operating Expense					$ 133	$ 132	419	424
Production and Ad Valorem Taxes					28	44	89	146
Transportation and Gathering Expense					74	40	185	119
Total					235	216	693	689
Other Operating (Income) Expense, Net
Midstream Gathering and Processing (Income) Expense, Net					4	1	10	8
Corporate Restructuring Expense	[1]				21	0	39	0
Stacked Drilling Rig Expense	[2]				13	0	20	0
Pension Plan Termination Expense	[3]				67	0	88	0
Rosetta Merger Expenses	[4]				71	0	73	0
Gain on Divestitures					0	30	0	72
Other, Net					(6)	(10)	(22)	(33)
Total					182	(19)	252	(31)
Other Non-Operating (Income) Expense, Net
Deferred Compensation Expense	[5]				(13)	(12)	(19)	0
Other (Income) Expense, Net					1	(1)	(1)	1
Total					(12)	$ (13)	(20)	$ 1
Accounts Receivable, Net
Commodity Sales					284		284		405
Joint Interest Billings					166		166		297
Other					140		140		171
Allowance for Doubtful Accounts					(19)		(19)		(16)
Total					571		571		857
Other Current Assets
Inventories, Materials and Supplies					116		116		81
Inventories, Crude Oil					28		28		24
Assets Held-for-Sale	[6]				78		78		180
Prepaid Expenses and Other Current Assets					59		59		40
Total					281		281		325
Other Noncurrent Assets
Investments in Unconsolidated Subsidiaries					427		427		325
Mutual Fund Investments					106		106		111
Commodity Derivative Assets					104		104		180
Other Assets					104		104		99
Total					741		741		715
Other Current Liabilities
Production and Ad Valorem Taxes					165		165		110
Income Taxes Payable					60		60		180
Deferred Income Taxes, Current					86		86		158
Accrued Benefit Costs, Current					30		30		125
Asset Retirement Obligations					141		141		81
Interest Payable					119		119		70
Current Portion of Capital Lease Obligations					57		57		68
Other					137		137		152
Total					795		795		944
Other Noncurrent Liabilities
Deferred Compensation Liabilities					229		229		218
Asset Retirement Obligations					746		746		670
Accrued Benefit Costs					17		17		24
Other					112		112		175
Total					$ 1,104		$ 1,104		$ 1,087
Common Stock Authorized prior to Certificate of Incorporation Amendment [Member]
Common stock, shares authorized (in shares) | shares					500,000,000		500,000,000
Common Stock Authorized after Stock Issuance [Member]
Common stock, shares authorized (in shares) | shares					1,000,000,000		1,000,000,000
Underwritten Public Offering [Member]
Underwritten public offering (in shares) | shares				21,000,000
Common stock, par value per share (in dollars per share) | $ / shares				$ 0.01
Sale of stock (in dollars per share) | $ / shares				$ 47.5
Over-Allotment Option [Member]
Underwritten public offering (in shares) | shares			3,150,000
Common stock, par value per share (in dollars per share) | $ / shares			$ 0.01
Rosetta Resources, Inc [Member]
Shares exchange in acquisition | shares		41,000,000
Other Operating (Income) Expense, Net
Rosetta Merger Expenses							$ 58
Rosetta Resources, Inc [Member] | Common Stock
Shares exchange in acquisition | shares		41,000,000
Exchange ratio of common shares for acquired company		0.542

[1] Amount represents expenses associated with the relocation of our personnel. The expenses primarily include the relocation of our Ardmore, Oklahoma office, as well as the consolidation of our Houston personnel to our corporate headquarters in Houston.

[2] Amount represents the day rate cost associated with drilling rigs under contract, but not currently being utilized in our US onshore drilling programs.

[3] Amount includes the expensing of the actuarial loss from AOCL related to the termination and re-measurement of our defined benefit pension plan.

[4] Amount represents expenses associated with the completion of the Rosetta Merger. See Note 3. Rosetta Merger

[5] Amounts represent decreases in the fair value of shares of our common stock held in a rabbi trust.

[6] (1) Assets held for sale at September 30, 2015 include our Tanin and Karish natural gas discoveries, offshore Israel. See Update on Core Area – Israel, above.