Stock-Based Compensation - Summary of Total Share Based Liabilities (Detail) - CAD CAD in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share based liabilities paid	CAD 90	CAD 29	CAD 26
Deferred Share Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share based liabilities paid	3	17	17
Performance Share Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share based liabilities paid	79	0	0
Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share based liabilities paid	CAD 8	CAD 12	CAD 9