Oil and Gas Properties (Narratives) (Details) $ in Billions	12 Months Ended
Dec. 31, 2015 USD ($) $ / Mcfe	Dec. 31, 2016 $ / Mcfe	Dec. 31, 2014 $ / Mcfe
Oil And Gas Property [Abstract]
DD&A per Mcfe \| $ / Mcfe	1.38	0.44	1.18
Ceiling test limitation \| $	$ 3.1

The excess of unamortized costs capitalized within a cost center, less related deferred income taxes, over the cost center ceiling limitation, which is charged to expense for oil and gas producing companies that use full cost method of accounting for investments in oil and gas producing properties.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 932
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-10(c)(4)(ii))
-URI http://asc.fasb.org/extlink&oid=82851474&loc=d3e511914-122862

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 932
-SubTopic 360
-Section S99
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=27015634&loc=d3e516453-122869

Name:	us-gaap_UnamortizedCostsCapitalizedLessRelatedDeferredIncomeTaxesExceedCeilingLimitationExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration