Segment Information - SPPC (Details) $ in Millions	3 Months Ended
	Mar. 31, 2024 USD ($) operatingSegment reportableSegment	Mar. 31, 2023 USD ($)	Dec. 31, 2023 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | operatingSegment	8
Operating revenue	$ 6,111	$ 6,346
Operating income (loss)	895	667
Interest expense	(691)	(586)
Allowance for equity funds	83	49
Interest and dividend income	116	86
Other, net	31	40
Income before income tax expense (benefit) and equity income (loss)	357	979
Assets	$ 140,235		$ 137,840
SPPC
Segment Reporting Information [Line Items]
Number of reportable segments | reportableSegment	2
Operating revenue	$ 346	400
Operating income (loss)	19	35
Interest expense	(20)	(16)
Capitalized interest	1	2
Allowance for equity funds	4	2
Interest and dividend income	4	7
Other, net	3	1
Income before income tax expense (benefit) and equity income (loss)	11	31
Assets	4,821		4,772
SPPC | Regulated electric
Segment Reporting Information [Line Items]
Regulated electric	260	304
Operating revenue	260	304
Operating income (loss)	12	25
Assets	4,239		4,251
SPPC | Regulated natural gas
Segment Reporting Information [Line Items]
Regulated natural gas	86	96
Operating revenue	86	96
Operating income (loss)	7	$ 10
Assets	461		454
SPPC | Other
Segment Reporting Information [Line Items]
Assets	$ 121		$ 67