ESTIMATES, SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES AND BALANCE SHEET DETAIL Estimates, Significant Accounting Policies and Balance Sheet Detail - Top Customers (Details)	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Entity-Wide Revenue, Major Customer, Percentage	100.00%	100.00%	100.00%
Ameren Corporation [Member]
Entity-Wide Revenue, Major Customer, Percentage	10.00%	13.00%	12.00%
Exelon Generation Company [Member] [Member]
Entity-Wide Revenue, Major Customer, Percentage	16.00%	0.00%	0.00%
Other Top 10 Customers
Entity-Wide Revenue, Major Customer, Percentage	28.00%	41.00%	38.00%
Remaining Customers
Entity-Wide Revenue, Major Customer, Percentage	46.00%	46.00%	50.00%

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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