EMPLOYEE BENEFIT PLANS - Weighted Average Asset Allocations (Details)	Dec. 31, 2015	Dec. 31, 2014
Plan's asset allocations by asset category
Weighted-average asset allocations by asset category (as a percent)	100.00%	100.00%
Cash
Plan's asset allocations by asset category
Weighted-average asset allocations by asset category (as a percent)	8.56%	11.54%
Fixed income securities
Plan's asset allocations by asset category
Weighted-average asset allocations by asset category (as a percent)	10.33%	12.46%
Equity
Plan's asset allocations by asset category
Weighted-average asset allocations by asset category (as a percent)	61.73%	76.00%
Inflation Hedges/Real Assets
Plan's asset allocations by asset category
Weighted-average asset allocations by asset category (as a percent)	5.03%	0.00%
Hedged Strategies
Plan's asset allocations by asset category
Weighted-average asset allocations by asset category (as a percent)	14.35%	0.00%