SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Public Utility, Property, Plant and Equipment [Line Items]
Period for probable revenue recovery			24 months
Increase in operating and maintenance expense	$ 1,611	$ 1,324	$ 5,001	$ 4,453
Increase in other income	$ 104	38	$ 318	98
Accounting Standards Update 2017-07
Public Utility, Property, Plant and Equipment [Line Items]
Increase in operating and maintenance expense		13		39
Increase in other income		$ 14		$ 41