SENIOR NOTES PAYABLE AND OTHER DEBT - Summary of Senior Notes Payables and Other Debt (Details) CAD in Thousands, $ in Thousands	Sep. 30, 2016 USD ($)	Sep. 30, 2016 CAD	May 31, 2016 CAD	Dec. 31, 2015 USD ($)	Dec. 31, 2015 CAD
Debt instruments
Principal amount outstanding	$ 11,317,837			$ 11,271,020
Deferred financing costs, net	(64,238)			(69,121)
Unamortized fair value adjustment	27,416			33,570
Unamortized discounts	(28,688)			(28,473)
Senior notes payable and other debt	11,252,327			11,206,996
Unsecured revolving credit facilities
Debt instruments
Principal amount outstanding	232,405			180,683
Unsecured revolving credit facilities | Canada, Dollars
Debt instruments
Principal amount outstanding | CAD		CAD 155,400			CAD 9,700
1.55% Senior Notes due 2016
Debt instruments
Principal amount outstanding	$ 0			$ 550,000
Interest rate	1.55%	1.55%		1.55%	1.55%
1.250% Senior Notes due 2017
Debt instruments
Principal amount outstanding	$ 300,000			$ 300,000
Interest rate	1.25%	1.25%		1.25%	1.25%
2.00% Senior Notes due 2018
Debt instruments
Principal amount outstanding	$ 700,000			$ 700,000
Interest rate	2.00%	2.00%		2.00%	2.00%
Unsecured Term Loan Due 2018
Debt instruments
Principal amount outstanding	$ 200,000			$ 200,000
Unsecured term loan due 2019
Debt instruments
Principal amount outstanding	373,353			468,477
4.00% Senior Notes due 2019
Debt instruments
Principal amount outstanding	$ 600,000			$ 600,000
Interest rate	4.00%	4.00%		4.00%	4.00%
3.00% Senior Notes, Series A due 2019
Debt instruments
Principal amount outstanding | CAD		CAD 304,715			CAD 289,038
Interest rate	3.00%	3.00%		3.00%	3.00%
2.700% Senior Notes due 2020
Debt instruments
Principal amount outstanding	$ 500,000			$ 500,000
Interest rate	2.70%	2.70%		2.70%	2.70%
Unsecured term loan due 2020
Debt instruments
Principal amount outstanding	$ 900,000			$ 900,000
4.750% Senior Notes due 2021
Debt instruments
Principal amount outstanding	$ 700,000			$ 700,000
Interest rate	4.75%	4.75%		4.75%	4.75%
4.25% Senior Notes due 2022
Debt instruments
Principal amount outstanding	$ 600,000			$ 600,000
Interest rate	4.25%	4.25%		4.25%	4.25%
3.25% Senior Notes due 2022
Debt instruments
Principal amount outstanding	$ 500,000			$ 500,000
Interest rate	3.25%	3.25%		3.25%	3.25%
3.300% Senior Notes due 2022
Debt instruments
Principal amount outstanding | CAD		CAD 190,447			CAD 180,649
Interest rate	3.30%	3.30%		3.30%	3.30%
3.125% Senior Notes due 2023
Debt instruments
Principal amount outstanding | CAD		CAD 400,000	CAD 400,000		CAD 0
Interest rate	3.125%	3.125%	3.125%
3.750% Senior Notes due 2024
Debt instruments
Principal amount outstanding	$ 400,000			$ 400,000
Interest rate	3.75%	3.75%		3.75%	3.75%
4.125% Senior Notes, Series B due 2024
Debt instruments
Principal amount outstanding | CAD		CAD 190,447			CAD 180,649
Interest rate	4.125%	4.125%		4.125%	4.125%
3.500% Senior Notes due 2025
Debt instruments
Principal amount outstanding	$ 600,000			$ 600,000
Interest rate	3.50%	3.50%		3.50%	3.50%
4.125% Senior Notes due 2026
Debt instruments
Principal amount outstanding	$ 500,000			$ 500,000
Interest rate	4.125%	4.125%		4.125%	4.125%
3.25% Senior Notes due 2026
Debt instruments
Principal amount outstanding	$ 450,000	CAD 450,000		$ 0
Interest rate	3.25%	3.25%
6.90% Senior Notes due 2037
Debt instruments
Principal amount outstanding	$ 52,400			$ 52,400
Interest rate	6.90%	6.90%		6.90%	6.90%
6.59% Senior Notes due 2038
Debt instruments
Principal amount outstanding	$ 22,973			$ 22,973
Interest rate	6.59%	6.59%		6.59%	6.59%
5.45% Senior Notes due 2043
Debt instruments
Principal amount outstanding	$ 258,750			$ 258,750
Interest rate	5.45%	5.45%		5.45%	5.45%
5.70% Senior Notes due 2043
Debt instruments
Principal amount outstanding	$ 300,000			$ 300,000
Interest rate	5.70%	5.70%		5.70%	5.70%
4.375% Senior Notes due 2045
Debt instruments
Principal amount outstanding	$ 300,000			$ 300,000
Interest rate	4.375%	4.375%		4.375%	4.375%
Mortgage loans and other
Debt instruments
Principal amount outstanding	$ 1,742,347			$ 1,987,401
Unsecured term loan
Debt instruments
Principal amount outstanding | CAD		CAD 573,400
Unsecured term loan | Canada, Dollars
Debt instruments
Principal amount outstanding | CAD		CAD 94,800
Mortgage Loans Held-for-Sale
Debt instruments
Principal amount outstanding	$ 66,000			$ 22,900