Income Taxes - SPPC - Components of Income Tax Expense (Benefit) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Components of Income Tax Expense (Benefit) [Line Items]
Current - Federal	$ (1,701)	$ (1,537)	$ (956)
Deferred - Federal	1,037	1,438	431
Investment tax credits	(4)	(3)	(6)
Total	(1,132)	308	(598)
SPPC
Components of Income Tax Expense (Benefit) [Line Items]
Current - Federal	5	3	19
Deferred - Federal	13	12	10
Investment tax credits	0	0	(1)
Total	$ 18	$ 15	$ 28