share-based compensation - Weighted average assumptions used (Details)	3 Months Ended	6 Months Ended	12 Months Ended
Jun. 30, 2020 Y $ / shares	Jun. 30, 2020 Y $ / shares	Dec. 31, 2020 CAD ($)
share-based compensation
Share option award fair value (per share option)	$ 0.63	$ 0.65
Risk free interest rate	0.37%	0.97%
Expected lives(1) (years)	4.25	4.25	7
Expected volatility	12.10%	12.30%
Dividend yield	5.10%	5.40%

The expected volatility of the share price used to calculate the fair value of the share options granted. Expected volatility is a measure of the amount by which a price is expected to fluctuate during a period. The measure of volatility used in option pricing models is the annualised standard deviation of the continuously compounded rates of return on the share over a period of time.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 2
-IssueDate 2019-01-01
-Paragraph 47
-Subparagraph a
-Clause i
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=2&code=ifrs-tx-2019-en-r&anchor=para_47_a_i&doctype=Standard
-URIDate 2019-03-27

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- Definition

The option life of share options granted.

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- Definition

The implied yield currently available on zero-coupon government issues of the country in whose currency the exercise price for share options granted is expressed, with a remaining term equal to the expected term of the option being valued (based on the option's remaining contractual life and taking into account the effects of expected early exercise). [Refer: Government [member]]

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- Definition

The percentage of an expected dividend used to calculate the fair value of share options granted.

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- Definition

The weighted average share price used as input to the option pricing model to calculate the fair value of share options granted. [Refer: Option pricing model [member]; Weighted average [member]]

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