Fair Value Measurements - MEC - Level 3 (Details) - MEC - Commodity - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Fair Value, Assets (Liabilities), Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 5	$ (5)
Changes in fair value recognized in regulatory assets	(13)	13
Settlements	3	(4)
Ending balance	$ (5)	$ 4