UTILITY PLANT AND JOINTLY-OWNED FACILITES (Amount of Lease Expense Incurred for Generation-Related Capital Leases) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Public Utility, Property, Plant and Equipment [Line Items]
Capital Lease Expense	$ 8	$ 12	$ 33
Interest Expense, Capital Leases
Public Utility, Property, Plant and Equipment [Line Items]
Interest Expense	3	4	10
Operating Expenses, Fuel
Public Utility, Property, Plant and Equipment [Line Items]
Interest Expense	0	0	1
Amortization of Capital Lease Assets	0	2	6
Operating Expenses, Amortization
Public Utility, Property, Plant and Equipment [Line Items]
Amortization of Capital Lease Assets	$ 5	$ 6	$ 16