Assets Held for Sale and Discontinued Operations - Summary of Assets and Liabilities Held for Sale (Detail) - CAD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Disclosure Of Assets And Liabilities Classified As Held For Sale [Line Items]
Noncurrent assets held for sale	$ 479	$ 1,048
Decommissioning Liabilities	151	$ 603
Deep Basin Segment [Member]
Disclosure Of Assets And Liabilities Classified As Held For Sale [Line Items]
Decommissioning Liabilities	151
Deep Basin Segment [Member] \| E&E Asset [Member]
Disclosure Of Assets And Liabilities Classified As Held For Sale [Line Items]
Noncurrent assets held for sale	47
Deep Basin Segment [Member] \| PP&E [Member]
Disclosure Of Assets And Liabilities Classified As Held For Sale [Line Items]
Noncurrent assets held for sale	$ 432

Line items represent concepts included in disclosure of assets and liabilities classified as held for sale.

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- Definition

The amount of liabilities included in disposal groups classified as held for sale. [Refer: Liabilities; Disposal groups classified as held for sale [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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- Definition

The amount of non-current assets or disposal groups classified as held for sale. [Refer: Disposal groups classified as held for sale [member]]

+ References

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