SHARE BASED COMPENSATION - Stock Option Plans - (Details)	12 Months Ended
Dec. 31, 2020 CAD ($)	Dec. 31, 2019 CAD ($) Y
SHARE BASED COMPENSATION
Option term (expiration period)	7 years
Vesting period	3 years
Active Stock Option Plan
SHARE BASED COMPENSATION
Option term (expiration period)	7 years
Vesting period	3 years
Annual dividend per share (dollars)	$ 1.10	$ 1.68
Risk-free interest rate	1.35%	1.78%
Expected life	5	5
Expected volatility	24.00%	26.00%
Weighted average fair value per option (dollars)	$ 4.51	$ 6.61

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.

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The option life of share options granted.

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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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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.

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

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The weighted average fair value of share options granted during the period at the measurement date. [Refer: Weighted average [member]]

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The contractual life of awards in a share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The vesting life of awards in a share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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