Change in Accounting Principle - Statement of Consolidated Operations (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015		Dec. 31, 2014
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Oil and gas production revenues									$ 5,367	$ 6,510	[1]	$ 12,795	[1]
Other									(34)	98	[1]	285	[1]
Gain (loss) on divestiture	$ 0	$ 5	$ 17	$ (1)	$ 77	$ (5)	$ 227	$ (18)	21	281	[1],[2]	(1,608)	[1],[2]
Exploration									473	2,771	[1]	2,499	[1]
General and administrative									410	380	[1]	453	[1]
Depreciation, depletion, and amortization									2,618	3,300	[2]	4,526	[2]
Impairments	144	951	238	42	5,100	4,100	660	2,100	1,103	9,472	[1],[2]	7,102	[1],[2]
Financing costs, net									417	511	[1]	413	[1]
Current income tax provision									391	435	[1]	1,281	[1]
Deferred income tax benefit									(833)	(1,445)	[1],[2]	(1,799)	[1],[2]
NET LOSS FROM CONTINUING OPERATIONS INCLUDING NONCONTROLLING INTEREST	(143)	(526)	(200)	(371)	(5,055)	(4,119)	(917)	(1,068)	(1,240)	(11,159)	[1]	(6,312)	[1]
Net income (loss) attributable to noncontrolling interest									132	(315)	[1]	341	[1]
Net loss from continuing operations attributable to common shareholders									(1,372)	(10,844)	[1]	(6,653)	[1]
Net loss from discontinued operations, net of tax									(33)	492	[1],[2]	(1,707)	[1],[2]
Net income (loss) attributable to common shareholders	$ (182)	$ (607)	$ (244)	$ (372)	$ (4,015)	$ (4,143)	$ (860)	$ (1,334)	$ (1,405)	$ (10,352)	[1]	$ (8,360)	[1]
Per Common Share
Basic and diluted net loss from continuing operations per share	$ (0.48)	$ (1.51)	$ (0.65)	$ (0.98)	$ (12.28)	$ (10.91)	$ (2.60)	$ (2.91)	$ (3.62)	$ (28.70)	[1]	$ (17.32)	[1]
Basic and diluted net loss from discontinued operations per share	0.00	(0.09)	0.00	0.00	1.66	(0.04)	0.32	(0.63)	(0.09)	1.30	[1]	(4.44)	[1]
Basic and diluted net loss per share	$ (0.48)	$ (1.60)	$ (0.65)	$ (0.98)	$ (10.62)	$ (10.95)	$ (2.28)	$ (3.54)	$ (3.71)	$ (27.40)	[1]	$ (21.76)	[1]
Other Comprehensive Income
Pension and postretirement benefit plan, net of tax									$ 7	$ (3)	[3],[4]	$ 0	[3]
COMPREHENSIVE INCOME (LOSS) ATTRIBUTABLE TO COMMON STOCK									(1,398)	(10,355)	[3]	(8,361)	[3]
Under Full Cost [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Oil and gas production revenues									5,208	6,383		12,691
Other									(38)	(76)		290
Gain (loss) on divestiture									17	59		(180)
Exploration									0	0		0
General and administrative										377		451
Depreciation, depletion, and amortization									3,570	29,372		9,720
Impairments									677	1,920		1,919
Financing costs, net									365	299		211
Current income tax provision									232	309		1,177
Deferred income tax benefit									(721)	(5,778)		(514)
NET LOSS FROM CONTINUING OPERATIONS INCLUDING NONCONTROLLING INTEREST									(1,361)	(22,757)		(3,472)
Net income (loss) attributable to noncontrolling interest									(26)	(409)		343
Net loss from continuing operations attributable to common shareholders									(1,335)	(22,348)		(3,815)
Net loss from discontinued operations, net of tax									(33)	(771)		(1,588)
Net income (loss) attributable to common shareholders									$ (1,368)	$ (23,119)		$ (5,403)
Per Common Share
Basic and diluted net loss from continuing operations per share									$ (3.52)	$ (59.16)		$ (9.93)
Basic and diluted net loss from discontinued operations per share									(0.09)	(2.04)		(4.13)
Basic and diluted net loss per share									$ (3.61)	$ (61.20)		$ (14.06)
Other Comprehensive Income
Pension and postretirement benefit plan, net of tax										$ 0
COMPREHENSIVE INCOME (LOSS) ATTRIBUTABLE TO COMMON STOCK									$ (1,361)	(23,119)		$ (5,404)
Change from Full Cost Method to Successful Efforts Method [Member] | Changes [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Oil and gas production revenues									159	127		104
Other									4	174		(5)
Gain (loss) on divestiture									4	222		(1,428)
Exploration									473	2,771		2,499
General and administrative										3		2
Depreciation, depletion, and amortization									(952)	(26,072)		(5,194)
Impairments									426	7,552		5,183
Financing costs, net									52	212		202
Current income tax provision									159	126		104
Deferred income tax benefit									(112)	4,333		(1,285)
NET LOSS FROM CONTINUING OPERATIONS INCLUDING NONCONTROLLING INTEREST									121	11,598		(2,840)
Net income (loss) attributable to noncontrolling interest									158	94		(2)
Net loss from continuing operations attributable to common shareholders									(37)	11,504		(2,838)
Net loss from discontinued operations, net of tax									0	1,263		(119)
Net income (loss) attributable to common shareholders									$ (37)	$ 12,767		$ (2,957)
Per Common Share
Basic and diluted net loss from continuing operations per share									$ (0.10)	$ 30.46		$ (7.39)
Basic and diluted net loss from discontinued operations per share									0.00	3.34		(0.31)
Basic and diluted net loss per share									$ (0.10)	$ 33.80		$ (7.70)
Other Comprehensive Income
Pension and postretirement benefit plan, net of tax										$ (3)
COMPREHENSIVE INCOME (LOSS) ATTRIBUTABLE TO COMMON STOCK									$ (37)	12,764		$ (2,957)
Oil [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Oil and gas production revenues									4,172	5,107	[1]	10,110	[1]
Oil [Member] | Under Full Cost [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Oil and gas production revenues									3,983	4,999		10,040
Oil [Member] | Change from Full Cost Method to Successful Efforts Method [Member] | Changes [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Oil and gas production revenues									189	108		70
Natural Gas [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Oil and gas production revenues									967	1,176	[1]	2,017	[1]
Natural Gas [Member] | Under Full Cost [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Oil and gas production revenues									997	1,157		1,983
Natural Gas [Member] | Change from Full Cost Method to Successful Efforts Method [Member] | Changes [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Oil and gas production revenues									(30)	19		34
Natural Gas Liquids [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Oil and gas production revenues									228	227	[1]	668	[1]
Natural Gas Liquids [Member] | Under Full Cost [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Oil and gas production revenues									228	227		668
Natural Gas Liquids [Member] | Change from Full Cost Method to Successful Efforts Method [Member] | Changes [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Oil and gas production revenues									0	0		0
Recurring [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Depreciation, depletion, and amortization									2,460	2,976		4,195
Recurring [Member] | Under Full Cost [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Depreciation, depletion, and amortization									1,974	3,531		4,388
Recurring [Member] | Change from Full Cost Method to Successful Efforts Method [Member] | Changes [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Depreciation, depletion, and amortization									486	(555)		(193)
Additional [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Depreciation, depletion, and amortization									0	0		0
Additional [Member] | Under Full Cost [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Depreciation, depletion, and amortization									1,438	25,517		5,001
Additional [Member] | Change from Full Cost Method to Successful Efforts Method [Member] | Changes [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Depreciation, depletion, and amortization									$ (1,438)	$ (25,517)		$ (5,001)

[1] Financial information for 2015 and 2014 has been recast to reflect retrospective application of the successful efforts method of accounting. See Note 1.

[2] Financial information for 2015 and 2014 has been recast to reflect retrospective application of the successful efforts method of accounting. See Note 1.

[3] Financial information for 2015 and 2014 has been recast to reflect retrospective application of the successful efforts method of accounting. See Note 1.

[4] Financial information for 2015, 2014, and 2013 has been recast to reflect retrospective application of the successful efforts method of accounting. See Note 1.