Revenues (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2021	Mar. 31, 2020
Total revenue from contracts with customers
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	$ 1,078	$ 1,014
Retail
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	919	909
Retail \| Residential
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	488	458
Retail \| Commercial and Industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	419	439
Retail \| Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	12	12
Wholesale Distribution [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	87	47
Transmission Services [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	18	13
Other
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	54	45
Alternative and Other [Member]
Disaggregation of Revenue [Line Items]
Alternative revenue and other	83	43
Regulated Electric \| Total revenue from contracts with customers
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	697	677
Regulated Electric \| Retail
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	584	602
Regulated Electric \| Retail \| Residential
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	246	238
Regulated Electric \| Retail \| Commercial and Industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	326	352
Regulated Electric \| Retail \| Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	12	12
Regulated Electric \| Wholesale Distribution [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	87	47
Regulated Electric \| Transmission Services [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	18	13
Regulated Electric \| Other
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	8	15
Regulated Electric \| Alternative and Other [Member]
Disaggregation of Revenue [Line Items]
Alternative revenue and other	36	35
Regulated Natural Gas \| Total revenue from contracts with customers
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	369	325
Regulated Natural Gas \| Retail
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	323	295
Regulated Natural Gas \| Retail \| Residential
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	239	217
Regulated Natural Gas \| Retail \| Commercial and Industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	84	78
Regulated Natural Gas \| Retail \| Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	0	0
Regulated Natural Gas \| Wholesale Distribution [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	0	0
Regulated Natural Gas \| Transmission Services [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	0	0
Regulated Natural Gas \| Other
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	46	30
Regulated Natural Gas \| Alternative and Other [Member]
Disaggregation of Revenue [Line Items]
Alternative revenue and other	46	7
All Other \| Total revenue from contracts with customers
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	12	12
All Other \| Retail
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	12	12
All Other \| Retail \| Residential
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	3	3
All Other \| Retail \| Commercial and Industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	9	9
All Other \| Retail \| Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	0	0
All Other \| Wholesale Distribution [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	0	0
All Other \| Transmission Services [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	0	0
All Other \| Other
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	0	0
All Other \| Alternative and Other [Member]
Disaggregation of Revenue [Line Items]
Alternative revenue and other	1	1
Total revenues
Disaggregation of Revenue [Line Items]
Total revenues	1,161	1,057
Total revenues \| Regulated Electric
Disaggregation of Revenue [Line Items]
Total revenues	733	712
Total revenues \| Regulated Natural Gas
Disaggregation of Revenue [Line Items]
Total revenues	415	332
Total revenues \| All Other
Disaggregation of Revenue [Line Items]
Total revenues	$ 13	$ 13

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