Segment Information - SPPC (Details) $ in Millions	12 Months Ended
	Dec. 31, 2021 USD ($) reportableSegment operatingSegment	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | operatingSegment	8
Revenues	$ 25,150	$ 20,952	$ 19,844
Operating income (loss)	5,327	4,291	4,150
Interest expense	2,118	2,021	1,912
Allowance for equity funds	126	165	173
Interest and dividend income	89	71	117
Other, net	(17)	88	97
Income (loss) before income tax expense (benefit) and equity income (loss)	5,294	7,471	2,414
Assets	$ 132,065	127,316	100,051
SPPC
Segment Reporting Information [Line Items]
Number of reportable segments | reportableSegment	2
Revenues	$ 965	854	889
Operating income (loss)	167	165	171
Interest expense	54	56	48
Allowance for borrowed funds	2	2	1
Allowance for equity funds	7	4	3
Interest and dividend income	9	4	3
Other, net	11	7	1
Income (loss) before income tax expense (benefit) and equity income (loss)	142	126	131
Assets	4,223	3,919	3,671
SPPC | Operating segments
Segment Reporting Information [Line Items]
Operating income (loss)	167	165	171
SPPC | Other
Segment Reporting Information [Line Items]
Assets	29	37	44
SPPC | Regulated electric
Segment Reporting Information [Line Items]
Revenues	848	738	770
SPPC | Regulated electric | Operating segments
Segment Reporting Information [Line Items]
Revenues	848	738	770
Operating income (loss)	148	147	150
Assets	3,829	3,540	3,319
SPPC | Regulated natural gas
Segment Reporting Information [Line Items]
Revenues	117	116	119
SPPC | Regulated natural gas | Operating segments
Segment Reporting Information [Line Items]
Revenues	117	116	119
Operating income (loss)	19	18	21
Assets	$ 365	$ 342	$ 308