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Derivatives Instruments (Concentration Risk) (Details) - CAD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Concentration Risk [Line Items]
Concentration Risk, maximum exposure	$ 1,119	$ 1,382
% of total exposure	100.00%	100.00%
Derivative Instruments (current and long-term)
Concentration Risk [Line Items]
Concentration Risk, maximum exposure	$ 87	$ 167
% of total exposure	8.00%	12.00%
Credit Concentration Risk
Concentration Risk [Line Items]
Concentration Risk, maximum exposure	$ 860	$ 1,035
Credit rating of A- or above | Derivative Instruments (current and long-term)
Concentration Risk [Line Items]
Concentration Risk, maximum exposure	$ 47	$ 130
% of total exposure	4.00%	9.00%
Credit rating of BBB- to BBB+ | Derivative Instruments (current and long-term)
Concentration Risk [Line Items]
Concentration Risk, maximum exposure	$ 8	$ 9
% of total exposure	1.00%	1.00%
Not rated | Derivative Instruments (current and long-term)
Concentration Risk [Line Items]
Concentration Risk, maximum exposure	$ 32	$ 28
% of total exposure	3.00%	2.00%
Receivables, net
Concentration Risk [Line Items]
Concentration Risk, maximum exposure	$ 1,032	$ 1,215
% of total exposure	92.00%	88.00%
Receivables, net | Other accounts receivable
Concentration Risk [Line Items]
Concentration Risk, maximum exposure	$ 184	$ 273
% of total exposure	16.00%	20.00%
Receivables, net | Trading group
Concentration Risk [Line Items]
Concentration Risk, maximum exposure	$ 192	$ 235
% of total exposure	17.00%	17.00%
Receivables, net | Credit rating of A- or above | Trading group
Concentration Risk [Line Items]
Concentration Risk, maximum exposure	$ 38	$ 49
% of total exposure	3.00%	4.00%
Receivables, net | Credit rating of BBB- to BBB+ | Trading group
Concentration Risk [Line Items]
Concentration Risk, maximum exposure	$ 59	$ 70
% of total exposure	5.00%	5.00%
Receivables, net | Credit rating of CCC- to CCC+ | Trading group
Concentration Risk [Line Items]
Concentration Risk, maximum exposure	$ 0	$ 8
% of total exposure	0.00%	0.00%
Receivables, net | Not rated | Trading group
Concentration Risk [Line Items]
Concentration Risk, maximum exposure	$ 95	$ 108
% of total exposure	9.00%	8.00%
Regulated utilities | Receivables, net
Concentration Risk [Line Items]
Concentration Risk, maximum exposure	$ 711	$ 707
% of total exposure	64.00%	51.00%
Regulated utilities | Receivables, net | Residential
Concentration Risk [Line Items]
Concentration Risk, maximum exposure	$ 344	$ 384
% of total exposure	31.00%	28.00%
Regulated utilities | Receivables, net | Commercial
Concentration Risk [Line Items]
Concentration Risk, maximum exposure	$ 170	$ 182
% of total exposure	15.00%	13.00%
Regulated utilities | Receivables, net | Industrial
Concentration Risk [Line Items]
Concentration Risk, maximum exposure	$ 66	$ 57
% of total exposure	6.00%	4.00%
Regulated utilities | Receivables, net | Other
Concentration Risk [Line Items]
Concentration Risk, maximum exposure	$ 131	$ 84
% of total exposure	12.00%	6.00%

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.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 21
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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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