NATURE OF OPERATIONS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Summary of Average Annual Depreciation Rates for All Utility Plants) (Details)	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Average Annual Depreciation Rates	2.97%	2.85%	2.83%

Composite depreciation rate for public utility plants in service.

No definition available.

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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration