Oil and Gas Properties (Details) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016 USD ($) $ / bbl $ / MMBTU	Sep. 30, 2016 USD ($) $ / bbl $ / MMBTU	Jun. 30, 2016 USD ($) $ / bbl $ / MMBTU	Mar. 31, 2016 USD ($) $ / bbl $ / MMBTU	Dec. 31, 2015 USD ($) $ / bbl $ / MMBTU	Sep. 30, 2015 USD ($) $ / bbl $ / MMBTU	Jun. 30, 2015 USD ($) $ / bbl $ / MMBTU	Mar. 31, 2015 USD ($) $ / bbl $ / MMBTU	Dec. 31, 2016 USD ($) $ / bbl $ / MMBTU	Dec. 31, 2015 USD ($) $ / bbl $ / MMBTU	Dec. 31, 2014 USD ($)
Oil and gas properties:
Capitalized Costs, Proved Properties	$ 21,998				$ 21,568				$ 21,998	$ 21,568
Capitalized Costs of Unproved Properties Excluded from Amortization, Cumulative	1,238				780				1,238	780
Capitalized Costs, Oil and Gas Producing Activities, Gross	23,236				22,348				23,236	22,348
Capitalized Costs, Accumulated Depreciation, Depletion, Amortization and Valuation Allowance Relating to Oil and Gas Producing Activities	(9,587)				(9,048)				(9,587)	(9,048)
Capitalized Costs, Accumulated Impairment Relating to Oil and Gas Producing Activities	(10,509)				(9,481)				(10,509)	(9,481)
Capitalized Costs, Oil and Gas Producing Activities, Net	3,140				3,819				3,140	3,819
Cost of oil and gas properties not subject to amortization
Acquisition costs	1,115								1,115
Exploration costs	4								4
Capitalized interest	119								119
Capitalized Costs of Unproved Properties Excluded from Amortization, Cumulative	$ 1,238				780				1,238	780
Oil and Gas Assets (Textuals) [Abstract]
Capitalization Of Internal Costs									$ 121	107	$ 199
Document Fiscal Year Focus									2016
Insurance Recoveries Decrease to Capital					$ 57					$ 57
Asset Impairment Charges								$ 4
Unweighted average commodity price of oil based on first day of month prices for prior twelve months | $ / bbl	42.82	41.73	43.14	46.23	50.11	59.09	71.56	82.60	42.82	50.11
Unweighted average commodity price of natural gas based on first day of month prices for prior twelve months | $ / MMBTU	2.48	2.28	2.24	2.40	2.59	3.06	3.39	3.88	2.48	2.59
Unamortized Costs Capitalized Less Related Deferred Income Taxes Exceed Ceiling Limitation Expense Gross	$ 0	$ 0	$ 522	$ 506	$ 702	$ 1,889	$ 1,521	$ 788	$ 1,028	$ 4,900
Unamortized Costs Capitalized Less Related Deferred Income Taxes Exceed Ceiling Limitations, Expense	0	0	522	506	651	1,222	958	496	1,028	3,327
Proceeds from Sale of Oil and Gas Property and Equipment									405	90	620
Value of Assets acquired									486	125	33
Asset Retirement Obligation, Liabilities Incurred									15	6	58
Granite Wash [Member]
Oil and Gas Assets (Textuals) [Abstract]
Proceeds from Sale of Oil and Gas Property and Equipment											588
Anadarko Basin Acquisition [Member]
Oil and Gas Assets (Textuals) [Abstract]
Value of Assets acquired									476
Costs Incurred, Acquisition of Unproved Oil and Gas Properties									398
Costs Incurred, Acquisition of Oil and Gas Properties with Proved Reserves									86
Texas Asset Sale [Member]
Oil and Gas Assets (Textuals) [Abstract]
Proceeds from Sale of Oil and Gas Property and Equipment									380
UNITED STATES
Oil and Gas Assets (Textuals) [Abstract]
Ceiling Limitation Exceed Unamortized Costs Capitalized	873								873
Unamortized Costs Capitalized Less Related Deferred Income Taxes Exceed Ceiling Limitation Expense Gross	0	0	501	461	656	1,817	1,521	788	962	4,782
Unamortized Costs Capitalized Less Related Deferred Income Taxes Exceed Ceiling Limitations, Expense	0	0	501	461	620	1,193	958	496	962	3,267
China [Member]
Oil and Gas Assets (Textuals) [Abstract]
Ceiling Limitation Exceed Unamortized Costs Capitalized	7								7
Unamortized Costs Capitalized Less Related Deferred Income Taxes Exceed Ceiling Limitation Expense Gross	0	0	21	45	46	72	0	0	66	118
Unamortized Costs Capitalized Less Related Deferred Income Taxes Exceed Ceiling Limitations, Expense	0	$ 0	$ 21	$ 45	$ 31	$ 29	$ 0	$ 0	66	60
Costs incurred in 2016 not subject to amortization [Member]
Oil and gas properties:
Capitalized Costs of Unproved Properties Excluded from Amortization, Cumulative	595								595
Cost of oil and gas properties not subject to amortization
Acquisition costs	540								540
Exploration costs	4								4
Capitalized interest	51								51
Capitalized Costs of Unproved Properties Excluded from Amortization, Cumulative	595								595
Costs incurred in 2015 and prior not subject to amortization [Member]
Oil and gas properties:
Capitalized Costs of Unproved Properties Excluded from Amortization, Cumulative	372								372
Cost of oil and gas properties not subject to amortization
Acquisition costs	339								339
Exploration costs	0								0
Capitalized interest	33								33
Capitalized Costs of Unproved Properties Excluded from Amortization, Cumulative	372								372
Costs incurred in 2014 not subject to amortization [Member]
Oil and gas properties:
Capitalized Costs of Unproved Properties Excluded from Amortization, Cumulative	197								197
Cost of oil and gas properties not subject to amortization
Acquisition costs	162								162
Exploration costs	0								0
Capitalized interest	35								35
Capitalized Costs of Unproved Properties Excluded from Amortization, Cumulative	197								197
Costs incurred in 2013 not subject to amortization [Member]
Oil and gas properties:
Capitalized Costs of Unproved Properties Excluded from Amortization, Cumulative	74								74
Cost of oil and gas properties not subject to amortization
Acquisition costs	74								74
Exploration costs	0								0
Capitalized interest	0								0
Capitalized Costs of Unproved Properties Excluded from Amortization, Cumulative	$ 74								74
Other Property [Member]
Oil and Gas Assets (Textuals) [Abstract]
Proceeds from Sale of Oil and Gas Property and Equipment									39	90	69
Value of Assets acquired									$ 7	$ 125	$ 33