Revenues Revenues (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Total revenue from contracts with customers
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	$ 5,320	$ 4,732	$ 4,840
Retail
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	4,114	3,830	3,934
Retail | Residential
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	1,722	1,667	1,613
Retail | C&I
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	2,353	2,124	2,283
Retail | Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	39	39	38
Wholesale
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	442	202	210
Transmission
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	242	238	216
Interchange
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	501	440	459
Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	21	22	21
Alternative and Other [Member]
Disaggregation of Revenue [Line Items]
Alternative revenue and other	436	369	272
Regulated Electric | Total revenue from contracts with customers
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	4,706	4,238	4,264
Regulated Electric | Retail
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	3,514	3,343	3,367
Regulated Electric | Retail | Residential
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	1,374	1,375	1,280
Regulated Electric | Retail | C&I
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	2,107	1,935	2,054
Regulated Electric | Retail | Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	33	33	33
Regulated Electric | Wholesale
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	442	202	210
Regulated Electric | Transmission
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	242	238	216
Regulated Electric | Interchange
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	501	440	459
Regulated Electric | Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	7	15	12
Regulated Electric | Alternative and Other [Member]
Disaggregation of Revenue [Line Items]
Alternative revenue and other	388	333	242
Regulated Natural Gas | Total revenue from contracts with customers
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	575	457	541
Regulated Natural Gas | Retail
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	561	450	532
Regulated Natural Gas | Retail | Residential
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	315	261	303
Regulated Natural Gas | Retail | C&I
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	246	189	229
Regulated Natural Gas | Retail | Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0
Regulated Natural Gas | Wholesale
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0
Regulated Natural Gas | Transmission
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	14	7	9
Regulated Natural Gas | Alternative and Other [Member]
Disaggregation of Revenue [Line Items]
Alternative revenue and other	48	36	30
All Other | Total revenue from contracts with customers
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	39	37	35
All Other | Retail
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	39	37	35
All Other | Retail | Residential
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	33	31	30
All Other | Retail | C&I
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0
All Other | Retail | Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	6	6	5
All Other | Wholesale
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0
All Other | Transmission
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0
All Other | Interchange
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0
All Other | Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0
All Other | Alternative and Other [Member]
Disaggregation of Revenue [Line Items]
Alternative revenue and other	0	0	0
Total revenues
Disaggregation of Revenue [Line Items]
Total revenues	5,756	5,101	5,112
Total revenues | Regulated Electric
Disaggregation of Revenue [Line Items]
Total revenues	5,094	4,571	4,506
Total revenues | Regulated Natural Gas
Disaggregation of Revenue [Line Items]
Total revenues	623	493	571
Total revenues | All Other
Disaggregation of Revenue [Line Items]
Total revenues	$ 39	$ 37	$ 35