Revenue from Contracts with Customers - SPPC (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Disaggregation of Revenue [Line Items]
Total Customer Revenue	$ 5,138	$ 4,357	$ 14,049	$ 11,190
Operating revenue	6,968	6,193	19,113	15,332
Other revenue
Disaggregation of Revenue [Line Items]
Operating revenue	87	94	326	314
Regulated
Disaggregation of Revenue [Line Items]
Total Customer Revenue	4,430	3,927	12,111	10,109
Regulated | Retail electric
Disaggregation of Revenue [Line Items]
Total Customer Revenue	3,096	2,981	7,615	7,214
Regulated | Retail gas
Disaggregation of Revenue [Line Items]
Total Customer Revenue	100	84	707	422
SPPC
Disaggregation of Revenue [Line Items]
Operating revenue	282	235	711	652
SPPC | Other revenue
Disaggregation of Revenue [Line Items]
Operating revenue	0	1	3	4
SPPC | Regulated electric
Disaggregation of Revenue [Line Items]
Operating revenue	266	220	636	569
SPPC | Regulated electric | Other revenue
Disaggregation of Revenue [Line Items]
Operating revenue	0	1	2	3
SPPC | Regulated natural gas
Disaggregation of Revenue [Line Items]
Operating revenue	16	15	75	83
SPPC | Regulated natural gas | Other revenue
Disaggregation of Revenue [Line Items]
Operating revenue	0	0	1	1
SPPC | Regulated
Disaggregation of Revenue [Line Items]
Total Customer Revenue	282	234	708	648
SPPC | Regulated | Wholesale, transmission and other
Disaggregation of Revenue [Line Items]
Total Customer Revenue	18	13	46	37
SPPC | Regulated | Regulated electric
Disaggregation of Revenue [Line Items]
Total Customer Revenue	266	219	634	566
SPPC | Regulated | Regulated electric | Wholesale, transmission and other
Disaggregation of Revenue [Line Items]
Total Customer Revenue	18	13	46	37
SPPC | Regulated | Regulated natural gas
Disaggregation of Revenue [Line Items]
Total Customer Revenue	16	15	74	82
SPPC | Regulated | Regulated natural gas | Wholesale, transmission and other
Disaggregation of Revenue [Line Items]
Total Customer Revenue	0	0	0	0
SPPC | Regulated | Total retail
Disaggregation of Revenue [Line Items]
Total Customer Revenue	264	221	662	611
SPPC | Regulated | Total retail | Regulated electric | Retail electric
Disaggregation of Revenue [Line Items]
Total Customer Revenue	248	206	588	529
SPPC | Regulated | Total retail | Regulated natural gas | Retail gas
Disaggregation of Revenue [Line Items]
Total Customer Revenue	16	15	74	82
SPPC | Regulated | Customer Revenue
Disaggregation of Revenue [Line Items]
Total Customer Revenue	263	220	660	608
SPPC | Regulated | Customer Revenue | Residential
Disaggregation of Revenue [Line Items]
Total Customer Revenue	102	87	279	262
SPPC | Regulated | Customer Revenue | Commercial
Disaggregation of Revenue [Line Items]
Total Customer Revenue	87	74	220	203
SPPC | Regulated | Customer Revenue | Industrial
Disaggregation of Revenue [Line Items]
Total Customer Revenue	73	58	157	140
SPPC | Regulated | Customer Revenue | Other retail
Disaggregation of Revenue [Line Items]
Total Customer Revenue	1	1	4	3
SPPC | Regulated | Customer Revenue | Regulated electric | Retail electric
Disaggregation of Revenue [Line Items]
Total Customer Revenue	247	205	586	526
SPPC | Regulated | Customer Revenue | Regulated electric | Retail electric | Residential
Disaggregation of Revenue [Line Items]
Total Customer Revenue	91	76	229	208
SPPC | Regulated | Customer Revenue | Regulated electric | Retail electric | Commercial
Disaggregation of Revenue [Line Items]
Total Customer Revenue	84	71	202	183
SPPC | Regulated | Customer Revenue | Regulated electric | Retail electric | Industrial
Disaggregation of Revenue [Line Items]
Total Customer Revenue	71	57	151	132
SPPC | Regulated | Customer Revenue | Regulated electric | Retail electric | Other retail
Disaggregation of Revenue [Line Items]
Total Customer Revenue	1	1	4	3
SPPC | Regulated | Customer Revenue | Regulated natural gas | Retail gas
Disaggregation of Revenue [Line Items]
Total Customer Revenue	16	15	74	82
SPPC | Regulated | Customer Revenue | Regulated natural gas | Retail gas | Residential
Disaggregation of Revenue [Line Items]
Total Customer Revenue	11	11	50	54
SPPC | Regulated | Customer Revenue | Regulated natural gas | Retail gas | Commercial
Disaggregation of Revenue [Line Items]
Total Customer Revenue	3	3	18	20
SPPC | Regulated | Customer Revenue | Regulated natural gas | Retail gas | Industrial
Disaggregation of Revenue [Line Items]
Total Customer Revenue	2	1	6	8
SPPC | Regulated | Customer Revenue | Regulated natural gas | Retail gas | Other retail
Disaggregation of Revenue [Line Items]
Total Customer Revenue	0	0	0	0
SPPC | Regulated | Distribution only service
Disaggregation of Revenue [Line Items]
Total Customer Revenue	1	1	2	3
SPPC | Regulated | Distribution only service | Regulated electric | Retail electric
Disaggregation of Revenue [Line Items]
Total Customer Revenue	1	1	2	3
SPPC | Regulated | Distribution only service | Regulated natural gas | Retail gas
Disaggregation of Revenue [Line Items]
Total Customer Revenue	$ 0	$ 0	$ 0	$ 0