Accounting Changes - Narrative (Details) - CAD CAD in Millions	12 Months Ended
Dec. 31, 2015	Dec. 31, 2014
Change in Accounting Estimate [Line Items]
Deferred income taxes	CAD 0	CAD 0
New Accounting Pronouncement, Early Adoption, Effect [Member]
Change in Accounting Estimate [Line Items]
Deferred income taxes		56
Accounting Standards Update 2015-07 [Member]
Change in Accounting Estimate [Line Items]
Net asset value investments no longer included in Level 2 and Level 3 fair value hierarchy	CAD 2,426	CAD 2,069

Amount after allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences and carryforwards, net of deferred tax liability attributable to taxable temporary differences expected to be realized or consumed within one year or operating cycle, if longer.

Reference 1: 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

Reference 2: 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 3: 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=6907707&loc=d3e32537-109319

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