Summary of Significant Accounting Policies - Intangible Assets and Goodwill (Details)	12 Months Ended
Dec. 31, 2016 CAD reporting_unit	Dec. 31, 2015 CAD
Finite-Lived Intangible Assets [Line Items]
Impairment test (years)	5 years
Number of reporting units \| reporting_unit	12
Goodwill impairment loss \| CAD	CAD 0	CAD 0
Minimum
Finite-Lived Intangible Assets [Line Items]
Intangible asset amortization rate	1.00%	1.00%
Maximum
Finite-Lived Intangible Assets [Line Items]
Intangible asset amortization rate	50.00%	50.00%
Computer software
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Service Life	4 years	4 years
Computer software \| Minimum
Finite-Lived Intangible Assets [Line Items]
Service Life Ranges	3 years	3 years
Computer software \| Maximum
Finite-Lived Intangible Assets [Line Items]
Service Life Ranges	10 years	10 years
Land, transmission and water rights
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Service Life	57 years	37 years
Land, transmission and water rights \| Minimum
Finite-Lived Intangible Assets [Line Items]
Service Life Ranges	30 years	30 years
Land, transmission and water rights \| Maximum
Finite-Lived Intangible Assets [Line Items]
Service Life Ranges	80 years	80 years
Other
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Service Life	15 years	15 years
Other \| Minimum
Finite-Lived Intangible Assets [Line Items]
Service Life Ranges	10 years	10 years
Other \| Maximum
Finite-Lived Intangible Assets [Line Items]
Service Life Ranges	104 years	104 years

Finite-Lived Intangible Assets, Amortization Rate

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- Definition

Goodwill, Impairment Test, Period

+ References

No definition available.

+ Details

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- Definition

Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ 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.

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- Definition

Remaining amortization period of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

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- Definition

Amount of loss from the write-down of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13854-109267

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13777-109266

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
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-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3602-108585

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-Publisher FASB
-Name Accounting Standards Codification
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-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

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- Definition

Number of reporting units tested for impairment of goodwill. A reporting unit is an operating segment or one level below an operating segment.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Reporting Unit
-URI http://asc.fasb.org/extlink&oid=6523643

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