PENSION AND OTHER POSTRETIREMENT BENEFIT PLANS - Assets Within Our Canadian Nonregisted Pension Plans (Details) - Non Registered Canadian Pension Plans	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Assets invested in pension plan, allocation percentage	100.00%	100.00%
Cash and short-term investments
Defined Benefit Plan Disclosure [Line Items]
Assets invested in pension plan, allocation percentage	53.40%	55.90%
Common and preferred stock
Defined Benefit Plan Disclosure [Line Items]
Assets invested in pension plan, allocation percentage	46.60%	44.10%