Supplemental Information To Statements Of Cash Flows (Narrative) (Details) - USD ($) $ in Millions			12 Months Ended
	Dec. 17, 2015	Mar. 07, 2014	Dec. 31, 2015
Powder River Basin [Member]
Supplemental Cash Flow [Line Items]
Cash payment to acquire interest	$ 300
General Partner And EnLink [Member]
Supplemental Cash Flow [Line Items]
Cash payment to acquire interest		$ 100
Equity Issued in Business Combination [Member] | EnLink [Member]
Supplemental Cash Flow [Line Items]
Noncash equity issuance in acquisition, value			$ 360
Equity Issued in Business Combination [Member] | Powder River Basin [Member] | Common Stock [Member]
Supplemental Cash Flow [Line Items]
Noncash equity issuance in acquisition, value	$ 199		$ 199