Risk Management - Impact of Fluctuating Commodity Prices and Interest Rates on Company'S Open Risk Management Positions (Detail) $ in Millions	6 Months Ended
Jun. 30, 2018 CAD ($)
Crude oil contracts [Member] \| Commodity Price Risk [Member]
Disclosure of Nature and Extent of Risks Arising from Financial Instruments [Line Items]
Sensitivity Range	± US$5.00 per bbl Applied to Brent, WTI and Condensate Hedges
Increase	$ (251)
Decrease	$ 246
Description of exposure to risk	Crude Oil Commodity Price
Crude oil differential contracts [Member] \| Commodity Price Risk [Member]
Disclosure of Nature and Extent of Risks Arising from Financial Instruments [Line Items]
Sensitivity Range	± US$2.50 per bbl Applied to Differential Hedges Tied to Production
Increase	$ 4
Decrease	$ (4)
Description of exposure to risk	Crude Oil Differential Price
Interest rate swap contract [Member] \| Interest Rate Risk [member]
Disclosure of Nature and Extent of Risks Arising from Financial Instruments [Line Items]
Sensitivity Range	± 50 Basis Points
Increase	$ 42
Decrease	$ (47)
Description of exposure to risk	Interest Rate Swaps

Change in price estimation under sensitivity analysis.

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- Definition

Theoretical impact to profit loss from decrease in crude oil sensitivity.

+ References

No definition available.

+ Details

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- Definition

Theoretical impact to profit loss from increase in crude oil sensitivity.

+ References

No definition available.

+ Details

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- Definition

The description of exposures to risks arising from financial instruments. [Refer: Financial instruments, class [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 7
-IssueDate 2017-01-01
-Paragraph 33
-Subparagraph a
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=7&date=2017-03-01&anchor=para_33_a&doctype=Standard
-URIDate 2017-03-09

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- Definition

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

+ References

No definition available.

+ Details

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