Supplemental Information To Statements Of Cash Flows (Narrative) (Details) - Equity Issued in Business Combination [Member] - USD ($) $ in Millions		12 Months Ended
Dec. 17, 2015	Dec. 31, 2015
EnLink [Member]
Supplemental Cash Flow [Line Items]
Noncash equity issuance in acquisition, value		$ 360
Powder River Basin [Member] \| Common Stock [Member]
Supplemental Cash Flow [Line Items]
Noncash equity issuance in acquisition, value	$ 199

Amount of equity interests of the acquirer, including instruments or interests issued or issuable in consideration for the business combination.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 30
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=6911251&loc=d3e6578-128477

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 30
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=6911251&loc=d3e6613-128477

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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