Fair Value Measurements - NPC - Level 3 (Details) - NPC - 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	$ (52)	$ (113)
Changes in fair value recognized in regulatory assets	(65)	(56)
Settlements	1	1
Ending balance	$ (116)	$ (168)