PENSION AND OTHER POSTRETIREMENT BENEFIT PLANS - Assets Within Our Nonregisted Pension Plans (Details) - Non Registered Canadian Pension Plans	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Assets invested in pension plan, allocation percentage	100.00%	100.00%
Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Assets invested in pension plan, allocation percentage	55.90%	52.80%
Equities
Defined Benefit Plan Disclosure [Line Items]
Assets invested in pension plan, allocation percentage	44.10%	47.20%