Long-term debt (Details 5) (Capital lease) - CAD CAD in Millions	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015
Capital lease obligations [Abstract]
Interest imputed on capital leases	CAD 95	CAD 118
Capital leases obligations
Capital lease obligations [Abstract]
Capital lease obligations maturity start year	2017
Capital lease obligations maturity end year	2037
Net carrying amount of properties which secures the capital lease obligations	CAD 403	603
Capital lease obligations collateral description	As at December 31, 2016, the capital lease obligations are secured by properties
Capital leases obligations \| Minimum [Member]
Capital lease obligations [Abstract]
Interest rate for capital lease obligations	0.70%
Capital leases obligations \| Maximum [Member]
Capital lease obligations [Abstract]
Interest rate for capital lease obligations	6.80%
Equipment lease assets [Member]
Capital lease obligations [Abstract]
Capital lease assets acquired in period	CAD 57	CAD 0

Latest year the outstanding debt instruments are required to be repaid in CCYY format.

No definition available.

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- Definition

Earliest year the outstanding debt instruments are required to be repaid in CCYY format.

+ References

No definition available.

+ Details

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- Definition

Amount necessary to reduce net minimum lease payments to present value for capital leases.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6455398&loc=d3e45280-112737

+ Details

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- Definition

Discussion of whether the debt instrument is secured or unsecured, and, if secured, a description of the collateral and guarantees required or provided.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=6479336&loc=d3e64711-112823

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- Definition

Amount of assets pledged to secure a debt instrument.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=6479336&loc=d3e64711-112823

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- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

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- References

No definition available.

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- Definition

Amount of acquisition of long-lived, physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

+ References

No definition available.

+ Details

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