SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Components of Net Periodic Benefit Cost) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost for benefits earned	$ 147	$ 132
Interest cost	161	178
Expected return on plan assets	(261)	(261)
Amortization of prior service cost	(1)	(1)
Amortization of net actuarial loss	1	1
Net periodic benefit cost	47	49
Regulatory account transfer	37	34
Total	84	83
Other Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost for benefits earned	16	15
Interest cost	13	16
Expected return on plan assets	(35)	(34)
Amortization of prior service cost	4	3
Amortization of net actuarial loss	(8)	(5)
Net periodic benefit cost	(10)	(5)
Regulatory account transfer	0	0
Total	$ (10)	$ (5)