DERIVATIVE FINANCIAL INSTRUMENTS On Income Statement (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Cash Flow Hedging [Member]
Derivative [Line Items]
increase decrease in derivatives affecting regulatory assets and liabilities	$ (2)	$ 2
Interest Rate Contract | Cash Flow Hedging [Member]
Derivative [Line Items]
increase decrease in derivatives affecting regulatory assets and liabilities	(2)	2
Not Designated as Hedging Instrument [Member] | Interest Rate Contract
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Deferred Accounts into Income		115
increase decrease in derivatives affecting regulatory assets and liabilities	(1)	65
Not Designated as Hedging Instrument [Member] | Interest Expense [Member] | Interest Rate Contract
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Deferred Accounts into Income	$ 0
Not Designated as Hedging Instrument [Member] | Other Income [Member] | Interest Rate Contract
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Deferred Accounts into Income		$ 115