Segment Information - SPPC (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) reportableSegment operatingSegment	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | operatingSegment			8
Operating revenue	$ 6,968	$ 6,193	$ 19,113	$ 15,332
Operating income	1,834	1,547	4,375	3,402
Interest expense	(531)	(504)	(1,593)	(1,490)
Allowance for equity funds	34	50	90	122
Interest and dividend income	18	17	65	57
Other, net	8	36	64	61
Income (loss) before income tax expense (benefit) and equity income (loss)	1,675	2,967	4,189	4,619
Assets	131,554		$ 131,554		$ 127,316
SPPC
Segment Reporting Information [Line Items]
Number of reportable segments | reportableSegment			2
Operating revenue	282	235	$ 711	652
Operating income	75	68	139	131
Interest expense	(14)	(14)	(41)	(42)
Capitalized interest	1	0	2	1
Allowance for equity funds	2	1	5	3
Interest and dividend income	3	1	6	3
Other, net	3	2	9	4
Income (loss) before income tax expense (benefit) and equity income (loss)	70	58	120	100
Assets	4,130		4,130		3,919
SPPC | Regulated electric
Segment Reporting Information [Line Items]
Regulated electric	266	220	636	569
Operating revenue	266	220	636	569
Operating income	74	66	126	119
Assets	3,744		3,744		3,540
SPPC | Regulated natural gas
Segment Reporting Information [Line Items]
Regulated natural gas	16	15	75	83
Operating revenue	16	15	75	83
Operating income	1	$ 2	13	$ 12
Assets	354		354		342
SPPC | Other
Segment Reporting Information [Line Items]
Assets	$ 32		$ 32		$ 37