Foreign Exchange (Gain) Loss, Net (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quantifying Misstatement in Current Year Financial Statements [Line Items]
Foreign exchange (gain) loss, net	$ (279)	$ (210)	$ 1,082
Translation Of U.S. Dollar Debt Issued From Canada [Member]
Quantifying Misstatement in Current Year Financial Statements [Line Items]
Immaterial Error Correction	The unrealized foreign exchange (gain) loss on translation of U.S. dollar financing debt issued from Canada for the year ended December 31, 2017 disclosed in the table above includes an out-of-period adjustment in respect of unrealized losses on a foreign-denominated capital lease obligation since December 2013. The cumulative impact recognized within foreign exchange (gain) loss in the Company's Consolidated Statement of Earnings for the year ended December 31, 2017 was $68 million, before tax ($47 million, after tax). Encana has determined that the adjustment is not material to the Consolidated Financial Statements for the year ended December 31, 2017 or any prior periods. Accordingly, comparative periods presented in the Consolidated Financial Statements have not been restated.
Foreign exchange (gain) loss, net	$ 68
Quantifying Misstatement in Current Year Financial Statements, Amount, after Tax	$ 47