Short-term Debt and Credit Facilities - SPPC (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Line of Credit Facility [Line Items]
Credit facilities	$ 11,281	$ 11,030
Short-term debt	(2,009)	(2,286)
Net credit facilities	8,683	8,154
SPPC
Line of Credit Facility [Line Items]
Credit facilities	250	250
Short-term debt	(159)	(45)
Net credit facilities	$ 91	$ 205
SPPC | Line of credit
Line of Credit Facility [Line Items]
Weighted average interest rate	0.86%	0.90%
SPPC | Secured credit facility, $250 million, expiring June 2024 | Line of credit
Line of Credit Facility [Line Items]
Credit facilities	$ 250
Debt to capitalization ratio	0.65