Change in Accounting Principle - Consolidated Balance Sheet (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015		Sep. 30, 2015	Dec. 31, 2014
Property and equipment - cost	$ 46,640	$ 46,150	[1]
Less: Accumulated depreciation, depletion, and amortization	(27,178)	(25,312)	[1]
Property and equipment, net	19,462	20,838	[1]
Total Assets	23,149	25,500	[1]	$ 31,239
Other current liabilities	1,071	1,223	[1]
Income taxes	1,783	2,529	[1]
Paid-in capital	12,421	12,619	[1]
Accumulated deficit	(3,203)	(1,980)	[1]
Accumulated other comprehensive loss	(119)	(119)	[1]
Noncontrolling interest	1,480	1,602	[1]
TOTAL EQUITY	7,949	9,490	[1]	$ 13,983	$ 20,541
Under Full Cost [Member]
Property and equipment - cost	95,107	93,825
Less: Accumulated depreciation, depletion, and amortization	(82,717)	(79,706)
Property and equipment, net	12,390	14,119
Total Assets	16,077	18,781
Income taxes	364	1,072
Paid-in capital	12,279	12,467
Accumulated deficit	(8,628)	(7,153)
Accumulated other comprehensive loss	(116)	(116)
Noncontrolling interest	1,391	1,662
TOTAL EQUITY	2,296	4,228			28,137
Change from Full Cost Method to Successful Efforts Method [Member] | Changes [Member]
Property and equipment - cost	(48,467)	(47,675)
Less: Accumulated depreciation, depletion, and amortization	55,539	54,394
Property and equipment, net	7,072	6,719
Total Assets	7,072	6,719
Income taxes	1,419	1,457
Paid-in capital	142	152
Accumulated deficit	5,425	5,173			$ (7,600)
Accumulated other comprehensive loss	(3)	(3)
Noncontrolling interest	89	(60)
TOTAL EQUITY	$ 5,653	$ 5,262

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