Fair Value Measurements - MEC - Level 3 (Details) - MEC - Commodity derivatives - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Fair Value, Assets (Liabilities), Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ (11)	$ 5	$ (5)
Changes in fair value recognized in net regulatory assets	(13)	(40)	37
Settlements	22	24	(27)
Ending balance	$ (2)	$ (11)	$ 5