FAIR VALUE MEASUREMENTS - Assets and Liabilities Measured on Recurring Basis (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Liabilities
Restricted cash	$ 26	$ 46
Recurring
Assets
Total assets	456	525
Liabilities
Total liabilities	(3)	(2)
Net assets	453	523
Recurring | FTRs | Derivative Liabilities
Liabilities
Total liabilities	(3)	(2)
Recurring | FTRs | Derivative Assets
Assets
Total assets	10	11
Recurring | Equity securities
Assets
Total assets	2	2
Recurring | U.S. state debt securities
Assets
Total assets	259	266
Recurring | Cash, cash equivalents and restricted cash
Assets
Total assets	144	206
Recurring | Other
Assets
Total assets	41	40
Recurring | Level 1
Assets
Total assets	146	208
Liabilities
Total liabilities	0	0
Net assets	146	208
Recurring | Level 1 | FTRs | Derivative Liabilities
Liabilities
Total liabilities	0	0
Recurring | Level 1 | FTRs | Derivative Assets
Assets
Total assets	0	0
Recurring | Level 1 | Equity securities
Assets
Total assets	2	2
Recurring | Level 1 | U.S. state debt securities
Assets
Total assets	0	0
Recurring | Level 1 | Cash, cash equivalents and restricted cash
Assets
Total assets	144	206
Recurring | Level 1 | Other
Assets
Total assets	0	0
Recurring | Level 2
Assets
Total assets	300	306
Liabilities
Total liabilities	0	0
Net assets	300	306
Recurring | Level 2 | FTRs | Derivative Liabilities
Liabilities
Total liabilities	0	0
Recurring | Level 2 | FTRs | Derivative Assets
Assets
Total assets	0	0
Recurring | Level 2 | Equity securities
Assets
Total assets	0	0
Recurring | Level 2 | U.S. state debt securities
Assets
Total assets	259	266
Recurring | Level 2 | Cash, cash equivalents and restricted cash
Assets
Total assets	0	0
Recurring | Level 2 | Other
Assets
Total assets	41	40
Recurring | Level 3
Assets
Total assets	10	11
Liabilities
Total liabilities	(3)	(2)
Net assets	7	9
Recurring | Level 3 | FTRs | Derivative Liabilities
Liabilities
Total liabilities	(3)	(2)
Recurring | Level 3 | FTRs | Derivative Assets
Assets
Total assets	10	11
Recurring | Level 3 | Equity securities
Assets
Total assets	0	0
Recurring | Level 3 | U.S. state debt securities
Assets
Total assets	0	0
Recurring | Level 3 | Cash, cash equivalents and restricted cash
Assets
Total assets	0	0
Recurring | Level 3 | Other
Assets
Total assets	$ 0	$ 0