Revenues (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Total revenue from contracts with customers
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	$ 960	$ 967	$ 1,008
Retail
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	788	785	841
Retail | Residential
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	322	313	328
Retail | C&I
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	460	466	506
Retail | Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	6	6	7
Interchange
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	168	177	158
Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	4	5	9
Alternative and Other [Member]
Disaggregation of Revenue [Line Items]
Alternative revenue and other	14	14	14
Regulated Electric | Total revenue from contracts with customers
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	843	833	867
Regulated Electric | Retail
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	675	655	705
Regulated Electric | Retail | Residential
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	258	240	255
Regulated Electric | Retail | C&I
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	411	409	444
Regulated Electric | Retail | Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	6	6	6
Regulated Electric | Interchange
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	168	177	158
Regulated Electric | Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	1	4
Regulated Electric | Alternative and Other [Member]
Disaggregation of Revenue [Line Items]
Alternative revenue and other	12	12	12
Regulated Natural Gas | Total revenue from contracts with customers
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	117	134	140
Regulated Natural Gas | Retail
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	113	130	135
Regulated Natural Gas | Retail | Residential
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	64	73	73
Regulated Natural Gas | Retail | C&I
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	49	57	62
Regulated Natural Gas | Retail | Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0
Regulated Natural Gas | Interchange
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0
Regulated Natural Gas | Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	4	4	5
Regulated Natural Gas | Alternative and Other [Member]
Disaggregation of Revenue [Line Items]
Alternative revenue and other	2	2	2
All Other | Total revenue from contracts with customers
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers			1
All Other | Retail
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers			1
All Other | Retail | Residential
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers			0
All Other | Retail | C&I
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers			0
All Other | Retail | Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers			1
All Other | Interchange
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers			0
All Other | Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers			0
All Other | Alternative and Other [Member]
Disaggregation of Revenue [Line Items]
Alternative revenue and other			0
Operating Segments
Disaggregation of Revenue [Line Items]
Total revenues	974	981	1,022
Operating Segments | Regulated Electric
Disaggregation of Revenue [Line Items]
Total revenues	855	845	879
Operating Segments | Regulated Natural Gas
Disaggregation of Revenue [Line Items]
Total revenues	$ 119	$ 136	142
Operating Segments | All Other
Disaggregation of Revenue [Line Items]
Total revenues			$ 1