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Derivatives Instruments (Credit Risk) (Narrative) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020 CAD ($) Days	Dec. 31, 2019 CAD ($)
Credit Derivatives [Line Items]
Concentration Risk, maximum exposure	$ 1,056	$ 1,119
Total cash deposits/collateral on hand	69	101
Receivables, net
Credit Derivatives [Line Items]
Concentration Risk, maximum exposure	958	1,032
Credit Concentration Risk
Credit Derivatives [Line Items]
Concentration Risk, maximum exposure	805	860
Total cash deposits/collateral on hand	251	259
Credit Concentration Risk | Receivables, net
Credit Derivatives [Line Items]
Financial assets, considered to be past due	123	115
Fair Value, Financial assets, considered to be past due	$ 101	$ 106
Average number of days financial asset outstanding | Days	70

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The average number of days outstanding for financial assets, considered o be past due.

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Amount of accounts receivable past due, classified as noncurrent.

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Maximum amount of loss due to credit risk that, based on the gross fair value of the financial instrument, the entity would incur if parties to the financial instruments that make up the concentration failed completely to perform according to the terms of the contracts and the collateral or other security, if any, for the amount due proved to be of no value to the entity.

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Amount of obligation to return cash collateral under master netting arrangements that have not been offset against derivative assets.

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