Fair Value Measurements - MEC - Level 3 (Details) - MEC - Commodity - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Fair Value, Assets (Liabilities), Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ (11)	$ 5
Changes in fair value recognized in regulatory assets	(4)	(13)
Settlements	9	3
Ending balance	$ (6)	$ (5)