Supplementary Financial Information on oil and natural gas exploration (Details)	Dec. 31, 2016	Dec. 31, 2015
SUPPLEMENTARY FINANCIAL INFORMATION Gas and Oil
Gas (MMCF) Proved developed and undeveloped reserves - 1/1/2016	2,604	2,866
Gas (MMCF) Purchase of oil and natural gas properties in place	0	0
Gas (MMCF) Discoveries and exclusions	0	0
Gas (MMCF) Revisions	615	(94)
Gas (MMCF) Sales of oil and gas properties in place	0	0
Gas (MMCF) Production	0	(168)
Gas (MMCF) Proved developed and undeveloped reserves - 12/31/2016	3,219	2,604
Gas (MMCF) Proved developed at beginning (of year)	504	698
Gas (MMCF) Proved developed reserves at end (of year)	1,051	504
SUPPLEMENTARY FINANCIAL INFORMATION Oil (MBBLS)(Details)
Oil (MBBLS) Proved developed and undeveloped reserves - 1/1/2015	58	139
Oil (MBBLS) Purchase of oil and natural gas properties in place	0	0
Oil (MBBLS) Discoveries and exclusions	0	0
Oil (MBBLS) Revisions	91	(69)
Oil (MBBLS) Sales of oil and gas properties in place	0	0
Oil (MBBLS) Production	0	(12)
Oil (MBBLS) Proved developed and undeveloped reserves 12/31/2015	149	58
Oil (MBBLS) Proved developed at beginning (of year)	59	70
Oil (MBBLS) Proved developed reserves at end( of year)	81	59