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Summary of Significant Accounting Policies - Income Taxes, Sales Taxes, and New Accounting Policies (Details) - CAD CAD in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Variable Interest Entity [Line Items]
Undistributed earnings on foreign subsidiaries	CAD 525	CAD 565
Hydroelectric Power Generation | BECOL
Variable Interest Entity [Line Items]
Long-term contract for electric power, term	50 years

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Amount of undistributed earnings of foreign subsidiaries intended to be permanently reinvested outside the country of domicile.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 740
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6487024&loc=d3e29054-158556

Reference 2: http://www.xbrl.org/2003/role/presentationRef
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 995
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-Section 50
-Paragraph 2
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Reference 4: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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