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Derivatives (Concentration Risk) (Details) - CAD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Concentration Risk [Line Items]
Concentration Risk	$ 1,382	$ 1,394
Accounts Receivable [Member]
Concentration Risk [Line Items]
Concentration Risk, Percentage	88.00%	81.00%
Concentration Risk	$ 1,215	$ 1,141
Accounts Receivable [Member] | A- Rating [Member]
Concentration Risk [Line Items]
Concentration Risk, Percentage	4.00%	4.00%
Concentration Risk	$ 49	$ 55
Accounts Receivable [Member] | BBB- to BBB+ Rating [Member]
Concentration Risk [Line Items]
Concentration Risk, Percentage	5.00%	4.00%
Concentration Risk	$ 70	$ 61
Accounts Receivable [Member] | Not Rated [Member]
Concentration Risk [Line Items]
Concentration Risk, Percentage	8.00%	7.00%
Concentration Risk	$ 108	$ 96
Accounts Receivable [Member] | CCC- to CCC+ [Member]
Concentration Risk [Line Items]
Concentration Risk, Percentage	0.00%	0.00%
Concentration Risk	$ 8	$ 0
Accounts Receivable, Residential [Member]
Concentration Risk [Line Items]
Concentration Risk, Percentage	28.00%	23.00%
Concentration Risk	$ 384	$ 326
Accounts Receivable, Commercial [Member]
Concentration Risk [Line Items]
Concentration Risk, Percentage	13.00%	11.00%
Concentration Risk	$ 182	$ 161
Accounts Receivable, Industrial [Member]
Concentration Risk [Line Items]
Concentration Risk, Percentage	4.00%	3.00%
Concentration Risk	$ 57	$ 46
Accounts Receivable, Other [Member]
Concentration Risk [Line Items]
Concentration Risk, Percentage	6.00%	7.00%
Concentration Risk	$ 84	$ 96
Regulated utilities [Member]
Concentration Risk [Line Items]
Concentration Risk, Percentage	51.00%	44.00%
Concentration Risk	$ 707	$ 629
Trading group [Member]
Concentration Risk [Line Items]
Concentration Risk, Percentage	17.00%	15.00%
Concentration Risk	$ 235	$ 212
Other Accounts Receivable [Member]
Concentration Risk [Line Items]
Concentration Risk, Percentage	20.00%	22.00%
Concentration Risk	$ 273	$ 300
Derivative [Member]
Concentration Risk [Line Items]
Concentration Risk, Percentage	12.00%	19.00%
Concentration Risk	$ 167	$ 253
Derivative [Member] | A- Rating [Member]
Concentration Risk [Line Items]
Concentration Risk, Percentage	9.00%	15.00%
Concentration Risk	$ 130	$ 207
Derivative [Member] | BBB- to BBB+ Rating [Member]
Concentration Risk [Line Items]
Concentration Risk, Percentage	1.00%	1.00%
Concentration Risk	$ 9	$ 10
Derivative [Member] | Not Rated [Member]
Concentration Risk [Line Items]
Concentration Risk, Percentage	2.00%	3.00%
Concentration Risk	$ 28	$ 36
Assets, Total [Member] | Credit Concentration Risk [Member]
Concentration Risk [Line Items]
Concentration Risk, Percentage	100.00%	100.00%

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://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 21
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13537-108611

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- Definition

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.

+ References

No definition available.

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- Definition

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 18
-URI http://asc.fasb.org/extlink&oid=84177426&loc=d3e6351-108592

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13531-108611

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=84177426&loc=d3e6404-108592

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-Name Accounting Standards Codification
-Topic 825
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-Section 50
-Paragraph 21
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