Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

+ Details

Name:	us-gaap_CostsIncurredOilAndGasPropertyAcquisitionExplorationAndDevelopmentActivitiesLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of gain (loss) on sale or disposal of assets, including but not limited to property plant and equipment, intangible assets and equity in securities of subsidiaries or equity method investee.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=68055307&loc=d3e2443-110228

+ Details

Name:	us-gaap_GainLossOnDispositionOfAssets1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of divestiture of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

+ Details

Name:	us-gaap_GoodwillWrittenOffRelatedToSaleOfBusinessUnit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The cash inflow from the sale of long-lived, physical assets that are used in the normal conduct of business to produce goods and services and not intended for resale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3179-108585

+ Details

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

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=eca_MontneyAreaAssetsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=eca_PiceanceAssetsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ConsolidationItemsAxis=us-gaap_CorporateNonSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=eca_EncanaPlaceOfficeBuildingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=eca_CanadianOperationsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ConsolidationItemsAxis=us-gaap_OperatingSegmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=eca_WheatlandAssetsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=eca_UsaOperationsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=eca_HaynesvilleAssetsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=eca_DjBasinAssetsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Acquisitions and Divestitures (Narrative) (Details) CAD in Millions, $ in Millions	3 Months Ended						12 Months Ended
	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 CAD	Dec. 31, 2016 USD ($)	Dec. 31, 2015 CAD	Dec. 31, 2015 USD ($)
Acquisitions and Divestitures [Line Items]
Proceeds from divestitures							$ 736		$ 1,262		$ 1,908
Gain (Loss) on Disposition of Assets	$ (1)	$ 406	$ (1)	$ (3)	$ 395	$ (2)	404		390		14
Montney Area Assets [Member]
Acquisitions and Divestitures [Line Items]
Goodwill allocated to divestiture									32
Piceance Assets [Member]
Acquisitions and Divestitures [Line Items]
Goodwill allocated to divestiture							216
Corporate, Non-segment [Member]
Acquisitions and Divestitures [Line Items]
Proceeds from divestitures											53
Corporate, Non-segment [Member] \| Encana Place Office Building [Member]
Acquisitions and Divestitures [Line Items]
Gain (Loss) on Disposition of Assets											12
Canadian Operations [Member] \| Operating Segments [Member]
Acquisitions and Divestitures [Line Items]
Proceeds from divestitures							41		456		959
Canadian Operations [Member] \| Operating Segments [Member] \| Wheatland Assets [Member]
Acquisitions and Divestitures [Line Items]
Proceeds from divestitures										CAD 557	467
Canadian Operations [Member] \| Operating Segments [Member] \| Montney Area Assets [Member]
Acquisitions and Divestitures [Line Items]
Proceeds from divestitures								CAD 600	455	CAD 450	355
Gain (Loss) on Disposition of Assets									394
Goodwill allocated to divestiture									32
USA Operations [Member] \| Operating Segments [Member]
Acquisitions and Divestitures [Line Items]
Proceeds from divestitures							695		806		896
USA Operations [Member] \| Operating Segments [Member] \| Haynesville Assets [Member]
Acquisitions and Divestitures [Line Items]
Proceeds from divestitures											$ 769
USA Operations [Member] \| Operating Segments [Member] \| DJ Basin Assets [Member]
Acquisitions and Divestitures [Line Items]
Proceeds from divestitures									633
USA Operations [Member] \| Operating Segments [Member] \| Piceance Assets [Member]
Acquisitions and Divestitures [Line Items]
Proceeds from divestitures							605		$ 135
Gain (Loss) on Disposition of Assets							406
Goodwill allocated to divestiture							$ 216