Income Taxes - Narrative (Details) $ in Millions, $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2021 CAD ($)	Sep. 30, 2020 CAD ($)	Sep. 30, 2021 CAD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 CAD ($)
Income Tax Disclosure [Abstract]
Effective tax rate	26.36%	23.97%	21.00%	21.00%	25.52%
Effective tax rate, excluding discrete items	24.60%	25.00%	24.60%	24.60%	25.00%
Foreign exchange loss (gain) on debt and lease liabilities	$ 46	$ (40)	$ (39)		$ 89
Merger termination fee	$ 0	$ 0	$ 845	$ 700	$ 0

Effective Income Tax Rate Reconciliation, Estimated Rate, Excluding Discrete Items, Percent

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- Definition

The aggregate foreign currency transaction gain or loss on long-term debt (both realized and unrealized) and lease liabilities included in determining net income for the reporting period net of hedging activity.

+ References

No definition available.

+ Details

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- Definition

Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=121826272&loc=d3e32687-109319

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- Definition

Gain (loss) related to the termination of a contract between the parties. The termination may be due to many causes including early termination of a lease by a lessee, a breach of contract by one party, or a failure to perform.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-URI http://asc.fasb.org/extlink&oid=123570139&loc=d3e3602-108585

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- References

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