Income Taxes - SPPC - Reconciliation of Effective Income Tax Rate (Details)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Schedule of Effective Income Tax Rate Reconciliation [Line Items]
Federal statutory income tax rate	21.00%	21.00%	21.00%
Effects of ratemaking	(11.00%)	(16.00%)	(4.00%)
Effective income tax rate	(87.00%)	(136.00%)	(21.00%)
SPPC
Schedule of Effective Income Tax Rate Reconciliation [Line Items]
Federal statutory income tax rate	21.00%	21.00%	21.00%
Effects of ratemaking	(9.00%)	(7.00%)	(8.00%)
Effective income tax rate	12.00%	14.00%	13.00%