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		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Total before tax [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from AOCL	CAD 47	CAD 65	CAD 141	CAD 196
Income tax recovery	(13)	(19)	(39)	(54)
Net of income tax	34	46	102	142
Amortization of prior service costs [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from AOCL	(2)	(2)	(5)	(5)
Recognition of net actuarial loss [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from AOCL	CAD 49	CAD 67	CAD 146	CAD 201