Income taxes (Details 3) (Formula 2) - CAD CAD in Millions	Dec. 31, 2015	Dec. 31, 2014
Income Taxes [Abstract]
Net noncurrent deferred income tax liabilities	CAD 8,105.0	CAD 6,834.0
Total net deferred income tax liability	CAD 8,105.0	CAD 6,834.0

Amount, after deferred tax asset, of deferred tax liability attributable to taxable differences, netted by jurisdiction and classified as noncurrent.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 45
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=37586315&loc=d3e31931-109318

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 45
-Paragraph 9
-URI http://asc.fasb.org/extlink&oid=37586315&loc=d3e31958-109318

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 45
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=37586315&loc=d3e31917-109318

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant