SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Components of Net Periodic Benefit Cost) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost for benefits earned	$ 129	$ 118	$ 257	$ 236
Interest cost	172	178	344	357
Expected return on plan assets	(256)	(192)	(511)	(385)
Amortization of prior service cost	(2)	(2)	(3)	(4)
Amortization of net actuarial loss	2	5	3	11
Net periodic benefit cost	45	107	90	215
Regulatory account transfer	39	(23)	77	(46)
Total	84	84	167	169
Other Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost for benefits earned	17	15	33	30
Interest cost	18	19	35	38
Expected return on plan assets	(32)	(25)	(65)	(49)
Amortization of prior service cost	3	4	7	8
Amortization of net actuarial loss	(2)	1	(3)	2
Net periodic benefit cost	4	14	7	29
Regulatory account transfer	0	0	0	0
Total	$ 4	$ 14	$ 7	$ 29