Revenue from Contracts with Customers - SPPC (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Disaggregation of Revenue [Line Items]
Total Customer Revenue	$ 4,199	$ 3,317	$ 8,911	$ 6,833
Operating revenue	6,064	4,612	12,145	9,139
Other revenue
Disaggregation of Revenue [Line Items]
Operating revenue	102	102	239	220
Regulated
Disaggregation of Revenue [Line Items]
Total Customer Revenue	3,587	2,969	7,681	6,182
Regulated | Retail electric
Disaggregation of Revenue [Line Items]
Total Customer Revenue	2,411	2,172	4,519	4,233
Regulated | Retail gas
Disaggregation of Revenue [Line Items]
Total Customer Revenue	109	104	607	338
SPPC
Disaggregation of Revenue [Line Items]
Operating revenue	209	185	429	417
SPPC | Other revenue
Disaggregation of Revenue [Line Items]
Operating revenue	1	1	2	3
SPPC | Electric
Disaggregation of Revenue [Line Items]
Operating revenue	189	165	370	349
SPPC | Electric | Other revenue
Disaggregation of Revenue [Line Items]
Operating revenue	1	1	1	2
SPPC | Natural Gas
Disaggregation of Revenue [Line Items]
Operating revenue	20	20	59	68
SPPC | 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	208	184	427	414
SPPC | Regulated | Wholesale, transmission and other
Disaggregation of Revenue [Line Items]
Total Customer Revenue	12	9	28	24
SPPC | Regulated | Electric
Disaggregation of Revenue [Line Items]
Total Customer Revenue	188	164	369	347
SPPC | Regulated | Electric | Wholesale, transmission and other
Disaggregation of Revenue [Line Items]
Total Customer Revenue	12	9	28	24
SPPC | Regulated | Natural Gas
Disaggregation of Revenue [Line Items]
Total Customer Revenue	20	20	58	67
SPPC | 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	196	175	399	390
SPPC | Regulated | Total retail | Electric | Retail electric
Disaggregation of Revenue [Line Items]
Total Customer Revenue	176	155	341	323
SPPC | Regulated | Total retail | Natural Gas | Retail gas
Disaggregation of Revenue [Line Items]
Total Customer Revenue	20	20	58	67
SPPC | Regulated | Customer Revenue
Disaggregation of Revenue [Line Items]
Total Customer Revenue	195	174	397	388
SPPC | Regulated | Customer Revenue | Residential
Disaggregation of Revenue [Line Items]
Total Customer Revenue	81	77	176	176
SPPC | Regulated | Customer Revenue | Commercial
Disaggregation of Revenue [Line Items]
Total Customer Revenue	69	60	132	129
SPPC | Regulated | Customer Revenue | Industrial
Disaggregation of Revenue [Line Items]
Total Customer Revenue	44	36	86	81
SPPC | Regulated | Customer Revenue | Other retail
Disaggregation of Revenue [Line Items]
Total Customer Revenue	1	1	3	2
SPPC | Regulated | Customer Revenue | Electric | Retail electric
Disaggregation of Revenue [Line Items]
Total Customer Revenue	175	154	339	321
SPPC | Regulated | Customer Revenue | Electric | Retail electric | Residential
Disaggregation of Revenue [Line Items]
Total Customer Revenue	68	63	138	132
SPPC | Regulated | Customer Revenue | Electric | Retail electric | Commercial
Disaggregation of Revenue [Line Items]
Total Customer Revenue	64	56	117	112
SPPC | Regulated | Customer Revenue | Electric | Retail electric | Industrial
Disaggregation of Revenue [Line Items]
Total Customer Revenue	42	34	81	75
SPPC | Regulated | Customer Revenue | Electric | Retail electric | Other retail
Disaggregation of Revenue [Line Items]
Total Customer Revenue	1	1	3	2
SPPC | Regulated | Customer Revenue | Natural Gas | Retail gas
Disaggregation of Revenue [Line Items]
Total Customer Revenue	20	20	58	67
SPPC | Regulated | Customer Revenue | Natural Gas | Retail gas | Residential
Disaggregation of Revenue [Line Items]
Total Customer Revenue	13	14	38	44
SPPC | Regulated | Customer Revenue | Natural Gas | Retail gas | Commercial
Disaggregation of Revenue [Line Items]
Total Customer Revenue	5	4	15	17
SPPC | Regulated | Customer Revenue | Natural Gas | Retail gas | Industrial
Disaggregation of Revenue [Line Items]
Total Customer Revenue	2	2	5	6
SPPC | Regulated | Customer Revenue | 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	2
SPPC | Regulated | Distribution only service | Electric | Retail electric
Disaggregation of Revenue [Line Items]
Total Customer Revenue	1	1	2	2
SPPC | Regulated | Distribution only service | Natural Gas | Retail gas
Disaggregation of Revenue [Line Items]
Total Customer Revenue	$ 0	$ 0	$ 0	$ 0