Income Taxes - SPPC - Components of Income Tax Expense (Benefit) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Components of Income Tax Expense (Benefit) [Line Items]
Current - Federal	$ (1,442)	$ (1,449)	$ (1,778)
Deferred - Federal	(356)	(462)	650
Total	(1,699)	(1,916)	(1,132)
SPPC
Components of Income Tax Expense (Benefit) [Line Items]
Current - Federal	72	(12)	5
Deferred - Federal	(57)	31	13
Investment tax credits	1	0	0
Total	$ 16	$ 19	$ 18