Income taxes (Details 3) (Formula 1) - CAD CAD in Millions	Dec. 31, 2016	Dec. 31, 2015
Income Taxes [Abstract]
Domestic	CAD 3,334	CAD 3,074
Foreign	5,139	5,031
Total net deferred income tax liability	CAD 8,473	CAD 8,105

Amount, after deferred tax asset, of deferred tax liability attributable to taxable differences without jurisdictional netting.

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=75116654&loc=d3e31931-109318

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=65882285&loc=d3e32537-109319

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