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Derivatives (Concentration Risk) (Details) - CAD CAD in Millions | 12 Months Ended
--- | ---
Dec. 31, 2016 | Dec. 31, 2015
Concentration Risk [Line Items] |  |
Concentration Risk, Percentage | 100.00% | 100.00%
Concentration Risk | CAD 1,290 | CAD 996
Accounts Receivable [Member] |  |
Concentration Risk [Line Items] |  |
Concentration Risk, Percentage | 78.00% | 58.00%
Concentration Risk | CAD 592 | CAD 374
Accounts Receivable [Member] | A- Rating [Member] |  |
Concentration Risk [Line Items] |  |
Concentration Risk, Percentage | 4.00% | 3.00%
Concentration Risk | CAD 52 | CAD 31
Accounts Receivable [Member] | BBB- to BBB+ Rating [Member] |  |
Concentration Risk [Line Items] |  |
Concentration Risk, Percentage | 5.00% | 2.00%
Concentration Risk | CAD 60 | CAD 22
Accounts Receivable [Member] | Not Rated [Member] |  |
Concentration Risk [Line Items] |  |
Concentration Risk, Percentage | 4.00% | 3.00%
Concentration Risk | CAD 57 | CAD 31
Accounts Receivable, Residential [Member] |  |
Concentration Risk [Line Items] |  |
Concentration Risk, Percentage | 24.00% | 20.00%
Concentration Risk | CAD 315 | CAD 189
Accounts Receivable, Commercial [Member] |  |
Concentration Risk [Line Items] |  |
Concentration Risk, Percentage | 13.00% | 10.00%
Concentration Risk | CAD 170 | CAD 103
Accounts Receivable, Industrial [Member] |  |
Concentration Risk [Line Items] |  |
Concentration Risk, Percentage | 3.00% | 3.00%
Concentration Risk | CAD 38 | CAD 29
Accounts Receivable, Other [Member] |  |
Concentration Risk [Line Items] |  |
Concentration Risk, Percentage | 5.00% | 5.00%
Concentration Risk | CAD 69 | CAD 53
Regulated utilities [Member] |  |
Concentration Risk [Line Items] |  |
Concentration Risk, Percentage | 45.00% | 38.00%
Concentration Risk | CAD 592 | CAD 374
Trading group [Member] |  |
Concentration Risk [Line Items] |  |
Concentration Risk, Percentage | 13.00% | 8.00%
Concentration Risk | CAD 169 | CAD 84
Other Accounts Receivable [Member] |  |
Concentration Risk [Line Items] |  |
Concentration Risk, Percentage | 20.00% | 12.00%
Concentration Risk | CAD 253 | CAD 120
Derivative [Member] |  |
Concentration Risk [Line Items] |  |
Concentration Risk, Percentage | 22.00% | 42.00%
Concentration Risk | CAD 276 | CAD 418
Derivative [Member] | A- Rating [Member] |  |
Concentration Risk [Line Items] |  |
Concentration Risk, Percentage | 20.00% | 34.00%
Concentration Risk | CAD 252 | CAD 340
Derivative [Member] | BBB- to BBB+ Rating [Member] |  |
Concentration Risk [Line Items] |  |
Concentration Risk, Percentage | 0.00% | 7.00%
Concentration Risk | CAD 1 | CAD 70
Derivative [Member] | Not Rated [Member] |  |
Concentration Risk [Line Items] |  |
Concentration Risk, Percentage | 2.00% | 1.00%
Concentration Risk | CAD 23 | CAD 8

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- 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=73719730&loc=d3e13537-108611 + Details
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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. + Details
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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=64851502&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=73719730&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=64851502&loc=d3e6404-108592 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 21 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=73719730&loc=d3e13537-108611 + Details
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