Segment Information - SPPC (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022 USD ($)	Jun. 30, 2021 USD ($)	Jun. 30, 2022 USD ($) reportableSegment operatingSegment	Jun. 30, 2021 USD ($)	Dec. 31, 2021 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | operatingSegment			8
Operating revenue	$ 6,612	$ 6,064	$ 12,642	$ 12,145
Operating income	1,207	1,208	2,443	2,541
Interest expense	(550)	(532)	(1,082)	(1,062)
Allowance for equity funds	42	30	80	56
Interest and dividend income	30	26	53	47
Other, net	(26)	48	(21)	56
Income (loss) before income tax expense (benefit) and equity income (loss)	3,249	2,760	2,779	2,514
Assets	135,295		$ 135,295		$ 132,065
SPPC
Segment Reporting Information [Line Items]
Number of reportable segments | reportableSegment			2
Operating revenue	258	209	$ 537	429
Operating income	23	25	61	64
Interest expense	(14)	(13)	(27)	(27)
Capitalized interest	0	1	1	1
Allowance for equity funds	2	2	4	3
Interest and dividend income	4	1	7	3
Other, net	0	2	2	6
Income (loss) before income tax expense (benefit) and equity income (loss)	15	18	48	50
Assets	4,415		4,415		4,223
SPPC | Regulated electric
Segment Reporting Information [Line Items]
Regulated electric	230	189	457	370
Operating revenue	230	189	457	370
Operating income	19	21	49	52
Assets	3,995		3,995		3,829
SPPC | Regulated natural gas
Segment Reporting Information [Line Items]
Regulated natural gas	28	20	80	59
Operating revenue	28	20	80	59
Operating income	4	$ 4	12	$ 12
Assets	385		385		365
SPPC | Other
Segment Reporting Information [Line Items]
Assets	$ 35		$ 35		$ 29