Segmented and Geographic Information - Geographic Information (Details) - CAD CAD in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues	CAD 1,637	CAD 1,554	CAD 1,450	CAD 1,591	CAD 1,687	CAD 1,709	CAD 1,651	CAD 1,665	CAD 6,232	CAD 6,712	CAD 6,620
Long-term assets excluding financial instruments, mortgages receivable and deferred tax assets	17,121				16,698				17,121	16,698	14,847
Canada [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues									4,473	4,662	4,655
Long-term assets excluding financial instruments, mortgages receivable and deferred tax assets	11,000				10,630				11,000	10,630	10,114
United States [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues									1,759	2,050	1,965
Long-term assets excluding financial instruments, mortgages receivable and deferred tax assets	CAD 6,121				CAD 6,068				CAD 6,121	CAD 6,068	CAD 4,733