SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Public Utility, Property, Plant and Equipment [Line Items]
Increase in operating and maintenance expense	$ 1,597	$ 1,517
Increase in other income	$ 108	34
Accounting Standards Update 2017-07
Public Utility, Property, Plant and Equipment [Line Items]
Increase in operating and maintenance expense		13
Increase in other income		$ 14