SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Components of Net Periodic Benefit Cost) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost for benefits earned	$ 128	$ 118	$ 385	$ 354
Interest cost	171	178	515	535
Expected return on plan assets	(255)	(193)	(766)	(578)
Amortization of prior service cost	(1)	(1)	(4)	(5)
Amortization of net actuarial loss	1	6	4	17
Net periodic benefit cost	44	108	134	323
Regulatory account transfer	41	(23)	118	(69)
Total	85	85	252	254
Other Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost for benefits earned	16	14	49	44
Interest cost	17	20	52	58
Expected return on plan assets	(33)	(24)	(98)	(73)
Amortization of prior service cost	4	4	11	12
Amortization of net actuarial loss	(1)	1	(4)	3
Net periodic benefit cost	3	15	10	44
Regulatory account transfer	0	0	0	0
Total	$ 3	$ 15	$ 10	$ 44