Change in Accounting Principle - Statement of Consolidated Operations (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Oil and Gas Production Revenues	$ 1,386	$ 1,991	$ 2,473	$ 3,650
Other	(21)	28	(24)	22
Gain on divestitures	17	227	16	209
Exploration	91	225	186	483
General and administrative	103	111	196	195
Depreciation, depletion and amortization	669	794	1,347	1,620
Impairments	173	512	173	2,424
Financing costs, net	104	117	209	241
Current income tax provision	144	900	134	848
Deferred income tax benefit	(225)	(169)	(226)	(1,318)
NET LOSS FROM CONTINUING OPERATIONS INCLUDING NONCONTROLLING INTEREST	(200)	(917)	(571)	(1,985)
Net income attributable to noncontrolling interest	44	63	45	91
Net loss from continuing operations attributable to common shareholders	(244)	(980)	(616)	(2,076)
Net income (loss) from discontinued operations, net of tax	0	120	0	(118)
NET LOSS ATTRIBUTABLE TO COMMON SHAREHOLDERS	$ (244)	$ (860)	$ (616)	$ (2,194)
Basic net loss from continuing operations per share	$ (0.65)	$ (2.60)	$ (1.63)	$ (5.50)
Basic net loss from discontinued operations per share	0.00	0.32	0.00	(0.31)
Basic net loss per share	(0.65)	(2.28)	(1.63)	(5.81)
Diluted net loss from continuing operations per share	(0.65)	(2.60)	(1.63)	(5.50)
Diluted net loss from discontinued operations per share	0.00	0.32	0.00	(0.31)
Diluted net loss per share	$ (0.65)	$ (2.28)	$ (1.63)	$ (5.81)
Change from Full Cost Method to Successful Efforts Method [Member]
Oil and Gas Production Revenues	$ 1,386	$ 1,991	$ 2,473	$ 3,650
Other	(21)	28	(24)	22
Gain on divestitures	17	227	16	209
Exploration	91	225	186	483
General and administrative				195
Depreciation, depletion and amortization			1,347	1,620
Impairments		512	173	2,424
Financing costs, net	104	117	209	241
Current income tax provision	144	900	134	848
Deferred income tax benefit	(225)	(169)	(226)	(1,318)
NET LOSS FROM CONTINUING OPERATIONS INCLUDING NONCONTROLLING INTEREST	(200)	(917)	(571)	(1,985)
Net income attributable to noncontrolling interest	44	63	45	91
Net loss from continuing operations attributable to common shareholders	(244)	(980)	(616)	(2,076)
Net income (loss) from discontinued operations, net of tax	0	120	0	(118)
NET LOSS ATTRIBUTABLE TO COMMON SHAREHOLDERS	$ (244)	$ (860)	$ (616)	$ (2,194)
Basic net loss from continuing operations per share	$ (0.65)	$ (2.60)	$ (1.63)	$ (5.50)
Basic net loss from discontinued operations per share	0.00	0.32	0.00	(0.31)
Basic net loss per share	(0.65)	(2.28)	(1.63)	(5.81)
Diluted net loss from continuing operations per share	(0.65)	(2.60)	(1.63)	(5.50)
Diluted net loss from discontinued operations per share	0.00	0.32	0.00	(0.31)
Diluted net loss per share	$ (0.65)	$ (2.28)	$ (1.63)	$ (5.81)
Change from Full Cost Method to Successful Efforts Method [Member] | Oil and gas property and equipment, Recurring [Member]
Depreciation, depletion and amortization	$ 629	$ 711	$ 1,265	$ 1,454
Change from Full Cost Method to Successful Efforts Method [Member] | Oil and gas property and equipment, Additional [Member]
Depreciation, depletion and amortization	0	0	0	0
Impairments	173
Change from Full Cost Method to Successful Efforts Method [Member] | Under Full Cost [Member]
Oil and Gas Production Revenues	1,339	1,952	2,399	3,590
Other	(22)	25	(27)	17
Gain on divestitures	5	0	3	0
Exploration	0	0	0	0
General and administrative				193
Depreciation, depletion and amortization			2,300	15,124
Impairments		0	105	0
Financing costs, net	90	63	180	133
Current income tax provision	25	665	61	580
Deferred income tax benefit	(120)	(1,525)	(301)	(4,460)
NET LOSS FROM CONTINUING OPERATIONS INCLUDING NONCONTROLLING INTEREST	(622)	(4,832)	(1,183)	(9,336)
Net income attributable to noncontrolling interest	(21)	36	(93)	51
Net loss from continuing operations attributable to common shareholders	(601)	(4,868)	(1,090)	(9,387)
Net income (loss) from discontinued operations, net of tax	0	(732)	0	(864)
NET LOSS ATTRIBUTABLE TO COMMON SHAREHOLDERS	$ (601)	$ (5,600)	$ (1,090)	$ (10,251)
Basic net loss from continuing operations per share	$ (1.58)	$ (12.89)	$ (2.88)	$ (24.88)
Basic net loss from discontinued operations per share	0.00	(1.94)	0.00	(2.29)
Basic net loss per share	(1.58)	(14.83)	(2.88)	(27.17)
Diluted net loss from continuing operations per share	(1.58)	(12.89)	(2.88)	(24.88)
Diluted net loss from discontinued operations per share	0.00	(1.94)	0.00	(2.29)
Diluted net loss per share	$ (1.58)	$ (14.83)	$ (2.88)	$ (27.17)
Change from Full Cost Method to Successful Efforts Method [Member] | Under Full Cost [Member] | Oil and gas property and equipment, Recurring [Member]
Depreciation, depletion and amortization	$ 507	$ 923	$ 1,059	$ 1,922
Change from Full Cost Method to Successful Efforts Method [Member] | Under Full Cost [Member] | Oil and gas property and equipment, Additional [Member]
Depreciation, depletion and amortization	671	5,816	1,159	13,036
Impairments	105
Change from Full Cost Method to Successful Efforts Method [Member] | Changes [Member]
Oil and Gas Production Revenues	47	39	74	60
Other	1	3	3	5
Gain on divestitures	12	227	13	209
Exploration	91	225	186	483
General and administrative				2
Depreciation, depletion and amortization			(953)	(13,504)
Impairments		512	68	2,424
Financing costs, net	14	54	29	108
Current income tax provision	119	235	73	268
Deferred income tax benefit	(105)	1,356	75	3,142
NET LOSS FROM CONTINUING OPERATIONS INCLUDING NONCONTROLLING INTEREST	422	3,915	612	7,351
Net income attributable to noncontrolling interest	65	27	138	40
Net loss from continuing operations attributable to common shareholders	357	3,888	474	7,311
Net income (loss) from discontinued operations, net of tax	0	852	0	746
NET LOSS ATTRIBUTABLE TO COMMON SHAREHOLDERS	$ 357	$ 4,740	$ 474	$ 8,057
Basic net loss from continuing operations per share	$ 0.93	$ 10.29	$ 1.25	$ 19.38
Basic net loss from discontinued operations per share	0.00	2.26	0.00	1.98
Basic net loss per share	0.93	12.55	1.25	21.36
Diluted net loss from continuing operations per share	0.93	10.29	1.25	19.38
Diluted net loss from discontinued operations per share	0.00	2.26	0.00	1.98
Diluted net loss per share	$ 0.93	$ 12.55	$ 1.25	$ 21.36
Change from Full Cost Method to Successful Efforts Method [Member] | Changes [Member] | Oil and gas property and equipment, Recurring [Member]
Depreciation, depletion and amortization	$ 122	$ (212)	$ 206	$ (468)
Change from Full Cost Method to Successful Efforts Method [Member] | Changes [Member] | Oil and gas property and equipment, Additional [Member]
Depreciation, depletion and amortization	(671)	(5,816)	(1,159)	(13,036)
Impairments	68
Oil [Member]
Oil and Gas Production Revenues	1,118	1,618	1,940	2,911
Oil [Member] | Change from Full Cost Method to Successful Efforts Method [Member]
Oil and Gas Production Revenues	1,118	1,618	1,940	2,911
Oil [Member] | Change from Full Cost Method to Successful Efforts Method [Member] | Under Full Cost [Member]
Oil and Gas Production Revenues	1,062	1,599	1,857	2,879
Oil [Member] | Change from Full Cost Method to Successful Efforts Method [Member] | Changes [Member]
Oil and Gas Production Revenues	56	19	83	32
Natural Gas [Member]
Oil and Gas Production Revenues	209	315	432	623
Natural Gas [Member] | Change from Full Cost Method to Successful Efforts Method [Member]
Oil and Gas Production Revenues	209	315	432	623
Natural Gas [Member] | Change from Full Cost Method to Successful Efforts Method [Member] | Under Full Cost [Member]
Oil and Gas Production Revenues	218	295	441	595
Natural Gas [Member] | Change from Full Cost Method to Successful Efforts Method [Member] | Changes [Member]
Oil and Gas Production Revenues	(9)	20	(9)	28
Natural Gas Liquids [Member]
Oil and Gas Production Revenues	59	58	101	116
Natural Gas Liquids [Member] | Change from Full Cost Method to Successful Efforts Method [Member]
Oil and Gas Production Revenues	59	58	101	116
Natural Gas Liquids [Member] | Change from Full Cost Method to Successful Efforts Method [Member] | Under Full Cost [Member]
Oil and Gas Production Revenues	59	58	101	116
Natural Gas Liquids [Member] | Change from Full Cost Method to Successful Efforts Method [Member] | Changes [Member]
Oil and Gas Production Revenues	$ 0	$ 0	$ 0	$ 0