Fair Value Measurements - NPC - Level 3 (Details) - NPC - Commodity Derivatives - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ (113)	$ 15	$ (8)
Changes in fair value recognized in net regulatory assets	(68)	(90)	(17)
Settlements	129	(38)	40
Ending balance	$ (52)	$ (113)	$ 15