Stock-based compensation - Weighted-Average Fair Value Assumptions (Details) - Stock Option Plan - $ / shares	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected option life (years)	4 years 9 months	4 years 9 months	5 years
Risk-free interest rate	0.53%	1.28%	2.22%
Expected stock price volatility	27.14%	23.14%	25.04%
Expected annual dividends (cad per share)	$ 0.760	$ 0.664	$ 0.524
Estimated forfeiture rate	2.62%	4.41%	6.05%
Weighted average grant date fair value of options granted during the year (cad per share)	$ 19.06	$ 13.80	$ 12.74

Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumption, Expected Dividend

No definition available.

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- Definition

Company estimated forfeitures based on past experience.

+ References

No definition available.

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- Definition

The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

+ References

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- Definition

The risk-free interest rate assumption that is used in valuing an option on its own shares.

+ References

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- Definition

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.

+ References

No definition available.

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- Definition

The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

+ References

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- Definition

Expected term of award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
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-Publisher FASB
-Name Accounting Standards Codification
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-URI http://asc.fasb.org/extlink&oid=122041274&loc=d3e301413-122809

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