Revenues (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019		Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Deferred Tax Assets, Tax Deferred Expense	$ 22	$ 29		$ 22
Net Deferred Tax Liablility [Member]
Disaggregation of Revenue [Line Items]
Deferred Tax Assets, Tax Deferred Expense	316	286	[1]
Regulated Electric [Member] | Retail
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	1,137	1,193		1,237
Regulated Electric [Member] | Retail | Residential
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	359	352		364
Regulated Electric [Member] | Retail | C&I
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	739	800		828
Regulated Electric [Member] | Retail | Other
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	39	41		45
Regulated Electric [Member] | Wholesale
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	345	361		426
Regulated Electric [Member] | Transmission
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	279	240		231
Regulated Electric [Member] | Other
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	4	3		13
Regulated Electric [Member] | Total revenue from contracts with customers
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	1,765	1,797		1,907
Regulated Electric [Member] | Alternative revenue and other
Disaggregation of Revenue [Line Items]
Alternative revenue and other	105	29		26
Operating Segments [Member] | Regulated Electric [Member]
Disaggregation of Revenue [Line Items]
Total revenues	$ 1,870	$ 1,826		$ 1,933

[1] Prior periods have been reclassified to conform to current year presentation.