Financial Instruments - Carrying Amounts and Reconciliation of Derivative Financial Instruments (Details) - CAD ($)	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Disclosure of detailed information about hedging instruments [line items]
Current portion of other long-term assets	$ 5,000,000	$ 5,000,000
Current portion of other long-term liabilities	(72,000,000)	(131,000,000)
Other long-term assets	135,000,000	131,000,000
Other long-term liabilities	(13,000,000)	(29,000,000)
Derivative financial asset (liability), net	55,000,000	(24,000,000)	$ 178,000,000
Cash flow hedges
Disclosure of detailed information about hedging instruments [line items]
Gain (loss) on hedge ineffectiveness	0	1,000,000	$ 3,000,000
Natural gas
Disclosure of detailed information about hedging instruments [line items]
Derivatives held for trading, (liability)	(41,000,000)	(45,000,000)
Crude oil
Disclosure of detailed information about hedging instruments [line items]
Derivatives held for trading, (liability)	(10,000,000)	0
Foreign currency forward contracts
Disclosure of detailed information about hedging instruments [line items]
Derivatives held for trading, (liability)	(13,000,000)	(7,000,000)
Foreign currency forward contracts \| Cash flow hedges
Disclosure of detailed information about hedging instruments [line items]
Cash flow hedges, asset (liability)	(21,000,000)	(108,000,000)
Cross currency swaps \| Cash flow hedges
Disclosure of detailed information about hedging instruments [line items]
Cash flow hedges, asset (liability)	$ 140,000,000	$ 136,000,000

Derivative Financial Assets (Liabilities) Held For Hedging

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- Definition

Derivative Financial Assets (Liabilities) Held For Trading

+ References

No definition available.

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- Definition

Derivative Financial Assets (Liabilities), Net

+ References

No definition available.

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- Definition

The amount of current derivative financial assets. [Refer: Derivative financial assets]

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 1
-IssueDate 2021-01-01
-Paragraph 55
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-URIDate 2021-03-24

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- Definition

The amount of current derivative financial liabilities. [Refer: Derivative financial liabilities]

+ References

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- Definition

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

+ References

No definition available.

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- Definition

The gain (loss) recognised in profit or loss on hedge ineffectiveness. [Refer: Gain (loss) on hedge ineffectiveness]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 7
-IssueDate 2021-01-01
-Paragraph 24C
-Subparagraph a
-Clause i
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=7&code=ifrs-tx-2021-en-r&anchor=para_24C_a_i&doctype=Standard
-URIDate 2021-03-24

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 7
-IssueDate 2021-01-01
-Paragraph 24C
-Subparagraph b
-Clause ii
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=7&code=ifrs-tx-2021-en-r&anchor=para_24C_b_ii&doctype=Standard
-URIDate 2021-03-24

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- Definition

The amount of non-current derivative financial assets. [Refer: Derivative financial assets]

+ References

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- Definition

The amount of non-current derivative financial liabilities. [Refer: Derivative financial liabilities]

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