Changes in Accumulated Other Comprehensive Loss ("AOCL") by Component - Amounts in Pension and Post-Retirement Defined Benefit Plans Reclassified from AOCL (Details) - CAD CAD in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Total before tax [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from AOCL	CAD 47	CAD 65	CAD 94	CAD 131
Income tax recovery	(13)	(17)	(26)	(35)
Net of income tax	34	48	68	96
Amortization of prior service costs [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from AOCL	(1)	(2)	(3)	(3)
Recognition of net actuarial loss [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from AOCL	CAD 48	CAD 67	CAD 97	CAD 134

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Amount before tax of reclassification adjustments of other comprehensive income (loss).

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Amount after tax of reclassification adjustments of other comprehensive income (loss).

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 14A
-URI http://asc.fasb.org/extlink&oid=66004124&loc=SL7669686-108580

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 55
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=66004921&loc=d3e1436-108581

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Amount of tax expense (benefit) of reclassification adjustment from accumulated other comprehensive income (loss).

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 20
-Section 45
-Paragraph 11
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-URI http://asc.fasb.org/extlink&oid=65896914&loc=d3e39076-109324

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-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=66004124&loc=d3e640-108580

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