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Derivatives Instruments (Concentration Risk) (Details) - CAD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Concentration Risk [Line Items]
Concentration Risk, maximum exposure	$ (1,056)	$ (1,119)
% of total exposure	(100.00%)	(100.00%)
Derivative Instruments (current and long-term)
Concentration Risk [Line Items]
Concentration Risk, maximum exposure	$ (98)	$ (87)
% of total exposure	(9.00%)	(8.00%)
Credit Concentration Risk
Concentration Risk [Line Items]
Concentration Risk, maximum exposure	$ (805)	$ (860)
Credit rating of A- or above | Derivative Instruments (current and long-term)
Concentration Risk [Line Items]
Concentration Risk, maximum exposure	$ (60)	$ (47)
% of total exposure	(6.00%)	(4.00%)
Credit rating of BBB- to BBB+ | Derivative Instruments (current and long-term)
Concentration Risk [Line Items]
Concentration Risk, maximum exposure	$ (13)	$ (8)
% of total exposure	(1.00%)	(1.00%)
Not rated | Derivative Instruments (current and long-term)
Concentration Risk [Line Items]
Concentration Risk, maximum exposure	$ (25)	$ (32)
% of total exposure	(2.00%)	(3.00%)
Receivables, net
Concentration Risk [Line Items]
Concentration Risk, maximum exposure	$ (958)	$ (1,032)
% of total exposure	(91.00%)	(92.00%)
Receivables, net | Classification as assets held for sale
Concentration Risk [Line Items]
Concentration Risk, maximum exposure	$ 0	$ (55)
% of total exposure	0.00%	(5.00%)
Receivables, net | Other accounts receivable
Concentration Risk [Line Items]
Concentration Risk, maximum exposure	$ (159)	$ (184)
% of total exposure	(15.00%)	(16.00%)
Receivables, net | Trading group
Concentration Risk [Line Items]
Concentration Risk, maximum exposure	$ (170)	$ (192)
% of total exposure	(16.00%)	(17.00%)
Receivables, net | Credit rating of A- or above | Trading group
Concentration Risk [Line Items]
Concentration Risk, maximum exposure	$ (54)	$ (38)
% of total exposure	(5.00%)	(3.00%)
Receivables, net | Credit rating of BBB- to BBB+ | Trading group
Concentration Risk [Line Items]
Concentration Risk, maximum exposure	$ (41)	$ (59)
% of total exposure	(4.00%)	(5.00%)
Receivables, net | Credit rating of CCC- to CCC+ | Trading group
Concentration Risk [Line Items]
Concentration Risk, maximum exposure	$ 0	$ 0
% of total exposure	0.00%	0.00%
Receivables, net | Not rated | Trading group
Concentration Risk [Line Items]
Concentration Risk, maximum exposure	$ (75)	$ (95)
% of total exposure	(7.00%)	(9.00%)
Regulated utilities | Receivables, net
Concentration Risk [Line Items]
Concentration Risk, maximum exposure	$ (629)	$ (711)
% of total exposure	(60.00%)	(64.00%)
Regulated utilities | Receivables, net | Residential
Concentration Risk [Line Items]
Concentration Risk, maximum exposure	$ (341)	$ (344)
% of total exposure	(32.00%)	(31.00%)
Regulated utilities | Receivables, net | Commercial
Concentration Risk [Line Items]
Concentration Risk, maximum exposure	$ (143)	$ (170)
% of total exposure	(14.00%)	(15.00%)
Regulated utilities | Receivables, net | Industrial
Concentration Risk [Line Items]
Concentration Risk, maximum exposure	$ (49)	$ (66)
% of total exposure	(5.00%)	(6.00%)
Regulated utilities | Receivables, net | Other
Concentration Risk [Line Items]
Concentration Risk, maximum exposure	$ (96)	$ (131)
% of total exposure	(9.00%)	(12.00%)

X

- Definition

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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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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