SHARE BASED COMPENSATION - Stock Option Plans - (Details)	12 Months Ended
Dec. 31, 2019 CAD ($)	Dec. 31, 2018 CAD ($) 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)	$ 1.68	$ 1.44
Risk-free interest rate	1.78%	2.03%
Expected life	5	5
Expected volatility	26.00%	24.00%
Weighted average fair value per option (dollars)	$ 6.61	$ 6.73
Executive and Key Contributor Stock Options
SHARE BASED COMPENSATION
Vesting period	3 years
Minimum \| Executive and Key Contributor Stock Options
SHARE BASED COMPENSATION
Option term (expiration period)	7 years
Maximum \| Executive and Key Contributor Stock Options
SHARE BASED COMPENSATION
Option term (expiration period)	10 years

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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