v3.26.1
Balance Sheet Components - Schedule of Regulatory Assets and Liabilities (Details) - USD ($)
$ in Millions
Jun. 30, 2026
Dec. 31, 2025
Regulated Asset Liability [Line Items]    
Regulatory assets $ 179 $ 135
Non-current regulatory assets 858 871
Regulatory liabilities 93 126
Non-current regulatory liabilities 811 818
Energy Commodity Derivatives [Member]    
Regulated Asset Liability [Line Items]    
Regulatory assets 28 18
Non-current regulatory assets 14 12
Deferred Climate Commitment Act Costs [Member]    
Regulated Asset Liability [Line Items]    
Regulatory assets 9 24
Non-current regulatory assets 0 0
Deferred Power Costs [Member]    
Regulated Asset Liability [Line Items]    
Regulatory assets 54 17
Non-current regulatory assets 39 71
Decoupling Surcharge [Member]    
Regulated Asset Liability [Line Items]    
Regulatory assets 38 27
Non-current regulatory assets 51 21
Unamortized Debt Repurchase Costs [Member]    
Regulated Asset Liability [Line Items]    
Regulatory assets 0 0
Non-current regulatory assets 5 5
Income Tax Related Assets [Member]    
Regulated Asset Liability [Line Items]    
Regulatory assets 0 0
Non-current regulatory assets 252 246
Pension and Other Postretirement Benefit Plans [Member]    
Regulated Asset Liability [Line Items]    
Regulatory assets 1 1
Non-current regulatory assets 72 72
Interest Rate Swaps [Member]    
Regulated Asset Liability [Line Items]    
Regulatory assets 0 0
Non-current regulatory assets 162 165
AFUDC Above FERC Allowed Rate [Member]    
Regulated Asset Liability [Line Items]    
Regulatory assets 0 0
Non-current regulatory assets 52 51
Settlement with Coeur d'Alene Tribe [Member]    
Regulated Asset Liability [Line Items]    
Regulatory assets 0 0
Non-current regulatory assets 34 34
Advanced Meter Infrastructure [Member]    
Regulated Asset Liability [Line Items]    
Regulatory assets 3 3
Non-current regulatory assets 19 20
Utility Plant Abandoned [Member]    
Regulated Asset Liability [Line Items]    
Regulatory assets 2 2
Non-current regulatory assets 11 31
Demand Side Management Programs [Member]    
Regulated Asset Liability [Line Items]    
Regulatory assets 0 0
Non-current regulatory assets 50 57
Colstrip [Member]    
Regulated Asset Liability [Line Items]    
Regulatory assets 2 2
Non-current regulatory assets 32 31
Wildfire Resiliency [Member]    
Regulated Asset Liability [Line Items]    
Regulatory assets 14 9
Non-current regulatory assets 21 17
Insurance Deferrals [Member]    
Regulated Asset Liability [Line Items]    
Regulatory assets 7 8
Non-current regulatory assets 7 8
Other Regulatory Assets [Member]    
Regulated Asset Liability [Line Items]    
Regulatory assets 21 24
Non-current regulatory assets 37 30
Other Income Tax Related Liabilities [Member]    
Regulated Asset Liability [Line Items]    
Regulatory liabilities 6 7
Non-current regulatory liabilities 48 51
Excess Deferred Income Taxes [Member]    
Regulated Asset Liability [Line Items]    
Regulatory liabilities 13 13
Non-current regulatory liabilities 260 266
Deferred Climate Commitment Act Revenues [Member]    
Regulated Asset Liability [Line Items]    
Regulatory liabilities 4 34
Non-current regulatory liabilities 0 0
Deferred Power Costs [Member]    
Regulated Asset Liability [Line Items]    
Regulatory liabilities 3 7
Non-current regulatory liabilities 5 0
Deferred Natural Gas Costs [Member]    
Regulated Asset Liability [Line Items]    
Regulatory liabilities 25 33
Non-current regulatory liabilities 0 0
Decoupling Rebate [Member]    
Regulated Asset Liability [Line Items]    
Regulatory liabilities 5 1
Non-current regulatory liabilities 0 3
Utility Plant Retirement Costs [Member]    
Regulated Asset Liability [Line Items]    
Regulatory liabilities 0 0
Non-current regulatory liabilities 467 468
Interest Rate Swaps [Member]    
Regulated Asset Liability [Line Items]    
Regulatory liabilities 0 0
Non-current regulatory liabilities 22 23
Provision For Rate Refund [Member]    
Regulated Asset Liability [Line Items]    
Regulatory liabilities 16 13
Non-current regulatory liabilities 0 0
Other Regulatory Liabilities [Member]    
Regulated Asset Liability [Line Items]    
Regulatory liabilities 21 18
Non-current regulatory liabilities $ 9 $ 7