Segmented and Geographic Information - Geographic Information (Details) - CAD CAD in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues	CAD 1,687	CAD 1,709	CAD 1,651	CAD 1,665	CAD 1,760	CAD 1,670	CAD 1,681	CAD 1,509	CAD 6,712	CAD 6,620	CAD 6,133
Long-term assets excluding financial instruments, mortgages receivable, and deferred tax assets	16,698				14,847				16,698	14,847	14,079
Canada [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues									4,662	4,655	4,330
Long-term assets excluding financial instruments, mortgages receivable, and deferred tax assets	10,630				10,114				10,630	10,114	9,842
United States [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues									2,050	1,965	1,803
Long-term assets excluding financial instruments, mortgages receivable, and deferred tax assets	CAD 6,068				CAD 4,733				CAD 6,068	CAD 4,733	CAD 4,237