Debt - Fair Value of Long Term Debt (Details) - USD ($) $ in Millions |
Jun. 30, 2026 |
Dec. 31, 2025 |
Jun. 30, 2025 |
|---|---|---|---|
| Debt Instrument [Line Items] | |||
| Gross long-term debt | $ 2,518.5 | $ 2,448.7 | $ 2,242.3 |
| Unamortized debt issuance costs | (16.1) | (15.9) | (14.1) |
| Long-term debt | 2,502.4 | ||
| NW Holdings | |||
| Debt Instrument [Line Items] | |||
| Gross long-term debt | 2,518.5 | 2,448.7 | 2,242.3 |
| Unamortized debt issuance costs | (16.1) | (15.9) | (14.1) |
| Long-term debt | 2,502.4 | 2,432.8 | 2,228.2 |
| Estimated fair value | 2,343.1 | 2,317.1 | 2,076.4 |
| NW Natural | |||
| Debt Instrument [Line Items] | |||
| Gross long-term debt | 1,544.7 | 1,544.7 | 1,374.7 |
| Unamortized debt issuance costs | (9.4) | (9.8) | (9.0) |
| Long-term debt | 1,535.3 | 1,534.9 | 1,365.7 |
| Estimated fair value | $ 1,346.7 | $ 1,383.1 | $ 1,193.2 |
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- Definition Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt. Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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- Definition Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable. Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition Amount, after deduction of unamortized premium (discount) and debt issuance cost, of long-term debt. Excludes lease obligation. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective bond issues. This does not include the amounts capitalized as part of the cost of the utility plant or asset. No definition available.
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