RISK MANAGEMENT AND FINANCIAL INSTRUMENTS - MARKET RISK (Details)	6 Months Ended
	Jun. 30, 2018 item
Interest rate contracts - short-term borrowings
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
Average swap rate, fixed (as a percent)	2.60%
Average swap rate, variable (as a percent)	2.20%
Interest rate contracts - long-term debt
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
Average swap rate, fixed (as a percent)	3.10%
Equity contracts
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
Number of forms of stock-based compensation with equity price risk	1