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Stock-based Compensation (Performance Share Unit Plan) (Details) - Performance Share Unit Plan - Employee - CAD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Share Unit Plans: Units
Share Unit Plans: Outstanding, Beginning Balance	1,381,100
Share Unit Plans: Granted including DRIP	271,185
Share Unit Plans: Exercised	(445,066)
Share Unit Plans: Forfeited	(80,690)
Share Unit Plans: Outstanding and exercisable, Ending Balance	1,126,529
Share Unit Plans: Weighted Average Grant Date Fair Value
Share Unit Plans: Weighted Average Grant Date Fair Value: Outstanding, Beginning Balance	$ 45.37
Share Unit Plans: Weighted Average Grant Date Fair Value: Granted including DRIP	53.14
Share Unit Plans: Weighted Average Grant Date Fair Value: Exercised	45.41
Share Unit Plans: Weighted Average Grant Date Fair Value: Forfeited	46.25
Share Unit Plans: Weighted Average Grant Date Fair Value: Outstanding and exercisable, Ending Balance	$ 47.16
Share Unit Plans: Aggregate intrinsic value
Share Unit Plans: Aggregate intrinsic value	$ 68.0	$ 88.0

X

- Definition

The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee exercised the right during the reporting period, in accordance with the terms of the arrangement.

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Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.

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The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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Per share or unit weighted-average fair value of nonvested award under share-based payment arrangement. Excludes share and unit options.

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Number of non-option equity instruments exercised by participants.

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Net number of non-option equity instruments granted to participants.

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Number of equity instruments other than options outstanding, including both vested and non-vested instruments.

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Intrinsic value of outstanding award under share-based payment arrangement. Excludes share and unit options.

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