SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Public Utility, Property, Plant and Equipment [Line Items]
Period for probable revenue recovery			24 months
Increase in operating and maintenance expense	$ 1,786	$ 1,605	$ 3,390	$ 3,129
Increase in other income	$ 106	26	$ 214	60
Accounting Standards Update 2017-07
Public Utility, Property, Plant and Equipment [Line Items]
Increase in operating and maintenance expense		13		26
Increase in other income		$ 13		$ 27