Short-term Debt and Credit Facilities - NPC (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Line of Credit Facility [Line Items]
Credit facilities	$ 10,873	$ 11,281
Short-term debt	(1,119)	(2,009)
Net credit facilities	9,134	8,683
NPC
Line of Credit Facility [Line Items]
Credit facilities	400	400
Short-term debt	0	(180)
Net credit facilities	400	220
Letters of credit outstanding	0	15
NPC | Line of credit
Line of Credit Facility [Line Items]
Short-term debt	$ 0	$ (180)
Weighted average interest rate	0.00%	0.86%
NPC | Secured credit facility, $400 million, expiring June 2025 | Line of credit
Line of Credit Facility [Line Items]
Credit facilities	$ 400
Debt to capitalization ratio	0.65