PENSION AND OTHER POST-EMPLOYMENT BENEFITS - Narrative (Details) - USD ($) $ in Millions		1 Months Ended	3 Months Ended			12 Months Ended
	Feb. 01, 2019	Jan. 31, 2018	Dec. 31, 2020	Sep. 30, 2020	Mar. 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Mark-to-market adjustment, net of capitalized amounts			$ 54		$ 423		$ 477	$ 676	$ 145
Increase in discount rate			0.29%				0.38%
Company contributions	$ 500
Future contributions made in current year		$ 750
Return seeking assets sold during period				$ 800			$ 1,400
Transmission companies
Defined Benefit Plan Disclosure [Line Items]
Mark-to-market adjustment, net of capitalized amounts			$ 21
Discontinued Operations
Defined Benefit Plan Disclosure [Line Items]
Mark-to-market adjustment, net of capitalized amounts								2	1
Pensions and OPEB
Defined Benefit Plan Disclosure [Line Items]
Actual return on plan assets							$ 1,225	$ 1,492	$ 371
Actual return on plan assets (percent)							14.70%	20.20%	(4.00%)
Expected return on plan assets							$ 651	$ 569	$ 605
Pension
Defined Benefit Plan Disclosure [Line Items]
Company contributions							24	521
Actual return on plan assets							$ 1,165	$ 1,419
Expected long-term return on plan assets							7.50%	7.50%	7.50%
Expected return on plan assets							$ 618	$ 540	$ 574
Increase in benefit obligation due to RP2014 mortality table							74
Pension | Forecast
Defined Benefit Plan Disclosure [Line Items]
Expected long-term return on plan assets						7.50%
OPEB
Defined Benefit Plan Disclosure [Line Items]
Company contributions							23	21
Actual return on plan assets							$ 60	$ 73
Expected long-term return on plan assets							7.50%	7.50%	7.50%
Expected return on plan assets							$ 33	$ 29	$ 31
Increase in benefit obligation due to RP2014 mortality table							2
OPEB | Transmission companies
Defined Benefit Plan Disclosure [Line Items]
Mark-to-market adjustment, net of capitalized amounts							$ 40	$ 47	$ 8
Minimum
Defined Benefit Plan Disclosure [Line Items]
Company contributions		$ 500