Revenue from Contracts with Customers - SPPC (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Disaggregation of Revenue [Line Items]
Operating revenue	$ 6,111	$ 6,346
Regulated | Regulated retail electric
Disaggregation of Revenue [Line Items]
Total Customer Revenue	2,714	2,688
Regulated | Regulated retail gas
Disaggregation of Revenue [Line Items]
Total Customer Revenue	339	392
SPPC
Disaggregation of Revenue [Line Items]
Operating revenue	346	400
SPPC | Regulated electric
Disaggregation of Revenue [Line Items]
Operating revenue	260	304
SPPC | Regulated natural gas
Disaggregation of Revenue [Line Items]
Operating revenue	86	96
SPPC | Regulated
Disaggregation of Revenue [Line Items]
Total Customer Revenue	346	400
SPPC | Regulated | Wholesale, transmission and other
Disaggregation of Revenue [Line Items]
Total Customer Revenue	21	32
SPPC | Regulated | Regulated electric
Disaggregation of Revenue [Line Items]
Total Customer Revenue	260	304
SPPC | Regulated | Regulated electric | Wholesale, transmission and other
Disaggregation of Revenue [Line Items]
Total Customer Revenue	21	32
SPPC | Regulated | Regulated natural gas
Disaggregation of Revenue [Line Items]
Total Customer Revenue	86	96
SPPC | Regulated | Regulated natural gas | Wholesale, transmission and other
Disaggregation of Revenue [Line Items]
Total Customer Revenue	0	0
SPPC | Regulated | Total retail
Disaggregation of Revenue [Line Items]
Total Customer Revenue	325	368
SPPC | Regulated | Total retail | Regulated electric | Regulated retail electric
Disaggregation of Revenue [Line Items]
Total Customer Revenue	239	272
SPPC | Regulated | Total retail | Regulated natural gas | Regulated retail gas
Disaggregation of Revenue [Line Items]
Total Customer Revenue	86	96
SPPC | Regulated | Customer Revenue
Disaggregation of Revenue [Line Items]
Total Customer Revenue	324	367
SPPC | Regulated | Customer Revenue | Residential
Disaggregation of Revenue [Line Items]
Total Customer Revenue	153	175
SPPC | Regulated | Customer Revenue | Commercial
Disaggregation of Revenue [Line Items]
Total Customer Revenue	106	118
SPPC | Regulated | Customer Revenue | Industrial
Disaggregation of Revenue [Line Items]
Total Customer Revenue	63	72
SPPC | Regulated | Customer Revenue | Other retail
Disaggregation of Revenue [Line Items]
Total Customer Revenue	2	2
SPPC | Regulated | Customer Revenue | Regulated electric | Regulated retail electric
Disaggregation of Revenue [Line Items]
Total Customer Revenue	238	271
SPPC | Regulated | Customer Revenue | Regulated electric | Regulated retail electric | Residential
Disaggregation of Revenue [Line Items]
Total Customer Revenue	100	115
SPPC | Regulated | Customer Revenue | Regulated electric | Regulated retail electric | Commercial
Disaggregation of Revenue [Line Items]
Total Customer Revenue	82	91
SPPC | Regulated | Customer Revenue | Regulated electric | Regulated retail electric | Industrial
Disaggregation of Revenue [Line Items]
Total Customer Revenue	55	63
SPPC | Regulated | Customer Revenue | Regulated electric | Regulated retail electric | Other retail
Disaggregation of Revenue [Line Items]
Total Customer Revenue	1	2
SPPC | Regulated | Customer Revenue | Regulated natural gas | Regulated retail gas
Disaggregation of Revenue [Line Items]
Total Customer Revenue	86	96
SPPC | Regulated | Customer Revenue | Regulated natural gas | Regulated retail gas | Residential
Disaggregation of Revenue [Line Items]
Total Customer Revenue	53	60
SPPC | Regulated | Customer Revenue | Regulated natural gas | Regulated retail gas | Commercial
Disaggregation of Revenue [Line Items]
Total Customer Revenue	24	27
SPPC | Regulated | Customer Revenue | Regulated natural gas | Regulated retail gas | Industrial
Disaggregation of Revenue [Line Items]
Total Customer Revenue	8	9
SPPC | Regulated | Customer Revenue | Regulated natural gas | Regulated retail gas | Other retail
Disaggregation of Revenue [Line Items]
Total Customer Revenue	1	0
SPPC | Regulated | Distribution only service
Disaggregation of Revenue [Line Items]
Total Customer Revenue	1	1
SPPC | Regulated | Distribution only service | Regulated electric | Regulated retail electric
Disaggregation of Revenue [Line Items]
Total Customer Revenue	1	1
SPPC | Regulated | Distribution only service | Regulated natural gas | Regulated retail gas
Disaggregation of Revenue [Line Items]
Total Customer Revenue	$ 0	$ 0