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Revenues (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
Revenues (Details) - USD ($) $ in Millions	Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
Total revenues
Disaggregation of Revenue [Line Items]
Total revenues	$ 282	$ 277	$ 663	$ 604
Regulated Electric \| Total revenues
Disaggregation of Revenue [Line Items]
Total revenues	257	253	555	512
Regulated Natural Gas \| Total revenues
Disaggregation of Revenue [Line Items]
Total revenues	25	24	108	92
Retail
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	213	217	519	480
Retail \| Residential
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	82	84	223	203
Retail \| C&I
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	129	132	292	274
Retail \| Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	2	1	4	3
Retail \| Regulated Electric
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	191	195	417	392
Retail \| Regulated Electric \| Residential
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	69	71	165	152
Retail \| Regulated Electric \| C&I
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	120	123	248	237
Retail \| Regulated Electric \| Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	2	1	4	3
Retail \| Regulated Natural Gas
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	22	22	102	88
Retail \| Regulated Natural Gas \| Residential
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	13	13	58	51
Retail \| Regulated Natural Gas \| C&I
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	9	9	44	37
Retail \| Regulated Natural Gas \| Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Interchange
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	65	59	136	119
Interchange \| Regulated Electric
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	63	57	132	116
Interchange \| Regulated Natural Gas
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	2	2	4	3
Total revenue from contracts with customers
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	278	276	655	599
Total revenue from contracts with customers \| Regulated Electric
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	254	252	549	508
Total revenue from contracts with customers \| Regulated Natural Gas
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	24	24	106	91
Alternative revenue and other
Disaggregation of Revenue [Line Items]
Alternative revenue and other	4	1	8	5
Alternative revenue and other \| Regulated Electric
Disaggregation of Revenue [Line Items]
Alternative revenue and other	3	1	6	4
Alternative revenue and other \| Regulated Natural Gas
Disaggregation of Revenue [Line Items]
Alternative revenue and other	$ 1	$ 0	$ 2	$ 1