v3.26.1
Significant Accounting Policies - Greenhouse Gas Allowances Narrative (Details) - USD ($)
$ in Millions
 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]    
CCI deferred costs $ 56.0 $ 40.7
Increase (decrease) in cloud-based software capital expenditure 5.1 3.9
Capitalized computer software, amortization 6.1 6.3
Location, Statement of Financial Position, Balance [Axis]: us-gaap:OtherAssetsCurrent    
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]    
Prepaid expense 27.6 23.4
Gas reserves 2.6 2.7
NW Natural | Location, Statement of Financial Position, Balance [Axis]: us-gaap:OtherAssetsCurrent    
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]    
Prepaid expense 14.4 13.5
Washington Climate Commitment Act compliance | NW Natural    
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]    
Regulatory liability 51.7  
Washington Climate Commitment Act Allowances    
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]    
Proceeds from other operating activity 51.7  
WASHINGTON    
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]    
Inventory, emissions allowances 83.2 54.5
CCI credits liability $ 56.0 $ 40.7