Revenues (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Retail
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	$ 3,547	$ 3,705	$ 3,465
Retail \| Residential
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	1,735	1,767	1,608
Retail \| C&I
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	1,764	1,888	1,809
Retail \| Other
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	48	50	48
Wholesale
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	212	166	175
Transmission
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	62	52	54
Other
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	181	139	139
Total revenue from contracts with customers
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	4,002	4,062	3,833
Alternative revenue and other
Disaggregation of Revenue [Line Items]
Alternative revenue and other	181	175	253
Regulated Electric \| Retail
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	2,633	2,635	2,599
Regulated Electric \| Retail \| Residential
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	1,073	1,006	991
Regulated Electric \| Retail \| C&I
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	1,512	1,579	1,560
Regulated Electric \| Retail \| Other
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	48	50	48
Regulated Electric \| Wholesale
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	212	166	175
Regulated Electric \| Transmission
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	62	52	54
Regulated Electric \| Other
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	56	32	55
Regulated Electric \| Total revenue from contracts with customers
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	2,963	2,885	2,883
Regulated Electric \| Alternative revenue and other
Disaggregation of Revenue [Line Items]
Alternative revenue and other	153	148	148
Regulated Natural Gas \| Retail
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	875	1,031	830
Regulated Natural Gas \| Retail \| Residential
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	650	750	606
Regulated Natural Gas \| Retail \| C&I
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	225	281	224
Regulated Natural Gas \| Retail \| Other
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	0	0	0
Regulated Natural Gas \| Wholesale
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	0	0	0
Regulated Natural Gas \| Transmission
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	0	0	0
Regulated Natural Gas \| Other
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	125	107	84
Regulated Natural Gas \| Total revenue from contracts with customers
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	1,000	1,138	914
Regulated Natural Gas \| Alternative revenue and other
Disaggregation of Revenue [Line Items]
Alternative revenue and other	24	23	101
All Other \| Retail
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	39	39	36
All Other \| Retail \| Residential
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	12	11	11
All Other \| Retail \| C&I
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	27	28	25
All Other \| Retail \| Other
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	0	0	0
All Other \| Wholesale
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	0	0	0
All Other \| Transmission
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	0	0	0
All Other \| Other
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	0	0	0
All Other \| Total revenue from contracts with customers
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	39	39	36
All Other \| Alternative revenue and other
Disaggregation of Revenue [Line Items]
Alternative revenue and other	4	4	4
Operating Segments
Disaggregation of Revenue [Line Items]
Total revenues	4,183	4,237	4,086
Operating Segments \| Regulated Electric
Disaggregation of Revenue [Line Items]
Total revenues	3,116	3,033	3,031
Operating Segments \| Regulated Natural Gas
Disaggregation of Revenue [Line Items]
Total revenues	1,024	1,161	1,015
Operating Segments \| All Other
Disaggregation of Revenue [Line Items]
Total revenues	$ 43	$ 43	$ 40

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