Segment Information - SPPC (Details) $ in Millions	3 Months Ended
	Mar. 31, 2022 USD ($) operatingSegment reportableSegment	Mar. 31, 2021 USD ($)	Dec. 31, 2021 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | operatingSegment	8
Operating revenue	$ 6,030	$ 6,081
Operating income	1,236	1,333
Interest expense	(532)	(530)
Allowance for equity funds	38	26
Interest and dividend income	23	21
Other, net	5	8
Income (loss) before income tax expense (benefit) and equity income (loss)	(470)	(246)
Assets	$ 131,469		$ 132,065
SPPC
Segment Reporting Information [Line Items]
Number of reportable segments | reportableSegment	2
Operating revenue	$ 279	220
Operating income	38	39
Interest expense	(13)	(14)
Capitalized interest	1	0
Allowance for equity funds	2	1
Interest and dividend income	3	2
Other, net	2	4
Income (loss) before income tax expense (benefit) and equity income (loss)	33	32
Assets	4,279		4,223
SPPC | Regulated electric
Segment Reporting Information [Line Items]
Regulated electric	227	181
Operating revenue	227	181
Operating income	30	31
Assets	3,869		3,829
SPPC | Regulated natural gas
Segment Reporting Information [Line Items]
Regulated natural gas	52	39
Operating revenue	52	39
Operating income	8	$ 8
Assets	375		365
SPPC | Other
Segment Reporting Information [Line Items]
Assets	$ 35		$ 29