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
	Mar. 31, 2016	Mar. 31, 2015
Total before tax [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from AOCL	CAD 47	CAD 66
Income tax recovery	(13)	(18)
Net of income tax	34	48
Amortization of prior service costs [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from AOCL	(2)	(1)
Recognition of net actuarial loss [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from AOCL	CAD 49	CAD 67