Significant Accounting Policies (Policies)	6 Months Ended
Jun. 30, 2026
Accounting Policies [Abstract]
Industry Regulation	Industry Regulation NW Holdings' principal business is to operate as a holding company for NW Natural, SiEnergy, NWN Water and its other subsidiaries. NW Natural's principal business is the distribution of natural gas, which is regulated by the Oregon Public Utility Commission (OPUC) and Washington Utilities and Transportation Commission (WUTC). NW Natural also has natural gas storage services, which are regulated by the Federal Energy Regulatory Commission (FERC), and to a certain extent by the OPUC and WUTC. SiEnergy's principal business is the distribution of natural gas in Texas; primarily in the Houston, Dallas and Austin metropolitan areas. SiEnergy also includes a natural gas transmission utility serving customers in the greater metropolitan areas of Dallas and Austin, Texas. SiEnergy's natural gas utilities are subject to regulation by the Railroad Commission of Texas and the cities in which it provides services. NWN Water's principal business is water and wastewater utility services. NWN Water's subsidiaries own water businesses, which are regulated by the public utility commission in the state in which the water utility is located, which is currently Oregon, Washington, Idaho, Texas and Arizona. Wastewater businesses, to the extent they are regulated, are generally regulated by the public utility commissions in the state in which the wastewater utility is located, which is currently Texas and Arizona. Accounting records and practices of the regulated businesses conform to the requirements and uniform system of accounts prescribed by these regulatory authorities in accordance with U.S. GAAP. The businesses in which customer rates are regulated have approved cost-based rates which are intended to allow such businesses to earn a reasonable return on invested capital. In applying regulatory accounting principles, NW Holdings and NW Natural capitalize or defer certain costs and revenues as regulatory assets and liabilities pursuant to orders of the applicable state public utility commission, which provide for the recovery of revenues or expenses from, or refunds to, utility customers in future periods, including a return or a carrying charge in certain cases.
New Accounting Standards	New Accounting Standards NW Holdings and NW Natural consider the applicability and impact of all accounting standards updates (ASUs) issued by the Financial Accounting Standards Board (FASB). ASUs not listed below were assessed and determined to be either not applicable or are expected to have minimal impact on consolidated financial position or results of operations. Recently Issued Accounting Pronouncements DISAGGREGATION OF EXPENSE DISCLOSURES. In November 2024, the FASB issued ASU 2024-03, which requires additional disclosures of disaggregated income statement expenses. The disclosures are required beginning with our annual report for the year ending December 31, 2027. The FASB issued ASU 2025-01 on January 6, 2025, to amend the effective date language of ASU 2024-03 clarifying that all public business entities are required to adopt the guidance in annual reporting periods beginning after December 15, 2026, and interim periods within annual reporting periods beginning after December 15, 2027. ASU 2025-01 did not impact the effective date of ASU 2024-03 for NW Holdings and NW Natural. The adoption of this standard is not anticipated to have an impact on our results of operations, liquidity, or capital resources. FINANCIAL INSTRUMENTS - CREDIT LOSSES. In July 2025, the FASB issued ASU 2025-05, which simplifies how entities estimate credit losses on current accounts receivable and current contract assets arising from revenue transactions under ASC 606. It introduced a practical expedient that allows all entities to assume that economic conditions at the balance sheet date remain unchanged for the life of the asset, eliminating the need for forward-looking forecasts. The Company elected the practical expedient and adopted this ASU effective January 1, 2026. The adoption of this standard did not have a material impact on our results of operations, liquidity or capital resources. IMPROVEMENTS TO INTANGIBLE ASSET ACCOUNTING AND DISCLOSURES. In September 2025, the FASB issued ASU 2025-06, Intangibles—Goodwill and Other—Internal-Use Software (Subtopic 350-40): Targeted Improvements to the Accounting for Internal-Use Software (“ASU 2025-06”). This ASU modernizes the accounting for software costs to adapt to an incremental and iterative software development method. ASU 2025-06 is effective for annual periods beginning after December 15, 2027, and may be applied using a prospective, modified prospective or retrospective transition approach. The adoption of this standard is not anticipated to have a material impact on our results of operations, liquidity or capital resources. INTERIM REPORTING. In December 2025, the FASB issued ASU 2025-11, which improves the guidance in Topic 270, Interim Reporting, by clarifying the current disclosure requirements for interim periods. The ASU adds to Topic 270 a principle that requires entities to disclose events since the end of the last annual reporting period that have a material impact on the entity. ASU 2025-11 is effective for interim reporting periods within annual reporting periods beginning after December 15, 2027. The adoption of this standard is not anticipated to have an impact on our results of operations, liquidity, or capital resources. CODIFICATION IMPROVEMENTS. In December 2025, the FASB issued ASU 2025-12, which makes changes to the Codification that clarify, correct errors, or make minor improvements. The amendments make the Codification easier to understand and apply. The amendments in this ASU are varied in nature and may affect the application of guidance in cases in which the original guidance may have been unclear. ASU 2025-12 is effective for annual reporting periods beginning after December 15, 2026, and interim reporting periods within those annual reporting periods. The adoption of this standard is not anticipated to have an impact on our results of operations, liquidity, or capital resources. ENVIRONMENTAL CREDITS AND ENVIRONMENTAL CREDIT OBLIGATIONS. In May 2026, the FASB issued ASU 2026-02, which provides recognition, measurement, presentation, and disclosure guidance for environmental credits and related obligations. The guidance is effective for annual periods beginning after December 15, 2027, and interim periods within those annual periods. The ASU is expected to be applicable to the extent the Company generates, purchases, receives, holds, sells, or uses environmental credits, or has regulatory compliance obligations that may be settled using environmental credits. The Company is currently evaluating the impact that the adoption of this standard will have on results of operations, liquidity or capital resources.

Significant Accounting Policies (Policies)

6 Months Ended

Jun. 30, 2026

NW Holdings' principal business is to operate as a holding company for NW Natural, SiEnergy, NWN Water and its other subsidiaries. NW Natural's principal business is the distribution of natural gas, which is regulated by the Oregon Public Utility Commission (OPUC) and Washington Utilities and Transportation Commission (WUTC). NW Natural also has natural gas storage services, which are regulated by the Federal Energy Regulatory Commission (FERC), and to a certain extent by the OPUC and WUTC. SiEnergy's principal business is the distribution of natural gas in Texas; primarily in the Houston, Dallas and Austin metropolitan areas. SiEnergy also includes a natural gas transmission utility serving customers in the greater metropolitan areas of Dallas and Austin, Texas. SiEnergy's natural gas utilities are subject to regulation by the Railroad Commission of Texas and the cities in which it provides services. NWN Water's principal business is water and wastewater utility services. NWN Water's subsidiaries own water businesses, which are regulated by the public utility commission in the state in which the water utility is located, which is currently Oregon, Washington, Idaho, Texas and Arizona. Wastewater businesses, to the extent they are regulated, are generally regulated by the public utility commissions in the state in which the wastewater utility is located, which is currently Texas and Arizona. Accounting records and practices of the regulated businesses conform to the requirements and uniform system of accounts prescribed by these regulatory authorities in accordance with U.S. GAAP. The businesses in which customer rates are regulated have approved cost-based rates which are intended to allow such businesses to earn a reasonable return on invested capital.

In applying regulatory accounting principles, NW Holdings and NW Natural capitalize or defer certain costs and revenues as regulatory assets and liabilities pursuant to orders of the applicable state public utility commission, which provide for the recovery of revenues or expenses from, or refunds to, utility customers in future periods, including a return or a carrying charge in certain cases.

New Accounting Standards

NW Holdings and NW Natural consider the applicability and impact of all accounting standards updates (ASUs) issued by the Financial Accounting Standards Board (FASB). ASUs not listed below were assessed and determined to be either not applicable or are expected to have minimal impact on consolidated financial position or results of operations.

Recently Issued Accounting Pronouncements

DISAGGREGATION OF EXPENSE DISCLOSURES. In November 2024, the FASB issued ASU 2024-03, which requires additional disclosures of disaggregated income statement expenses. The disclosures are required beginning with our annual report for the year ending December 31, 2027. The FASB issued ASU 2025-01 on January 6, 2025, to amend the effective date language of ASU 2024-03 clarifying that all public business entities are required to adopt the guidance in annual reporting periods beginning after December 15, 2026, and interim periods within annual reporting periods beginning after December 15, 2027. ASU 2025-01 did not impact the effective date of ASU 2024-03 for NW Holdings and NW Natural. The adoption of this standard is not anticipated to have an impact on our results of operations, liquidity, or capital resources.

FINANCIAL INSTRUMENTS - CREDIT LOSSES. In July 2025, the FASB issued ASU 2025-05, which simplifies how entities estimate credit losses on current accounts receivable and current contract assets arising from revenue transactions under ASC 606. It introduced a practical expedient that allows all entities to assume that economic conditions at the balance sheet date remain unchanged for the life of the asset, eliminating the need for forward-looking forecasts. The Company elected the practical expedient and adopted this ASU effective January 1, 2026. The adoption of this standard did not have a material impact on our results of operations, liquidity or capital resources.

IMPROVEMENTS TO INTANGIBLE ASSET ACCOUNTING AND DISCLOSURES. In September 2025, the FASB issued ASU 2025-06, Intangibles—Goodwill and Other—Internal-Use Software (Subtopic 350-40): Targeted Improvements to the Accounting for Internal-Use Software (“ASU 2025-06”). This ASU modernizes the accounting for software costs to adapt to an incremental and iterative software development method. ASU 2025-06 is effective for annual periods beginning after December 15, 2027, and may be applied using a prospective, modified prospective or retrospective transition approach. The adoption of this standard is not anticipated to have a material impact on our results of operations, liquidity or capital resources.

INTERIM REPORTING. In December 2025, the FASB issued ASU 2025-11, which improves the guidance in Topic 270, Interim Reporting, by clarifying the current disclosure requirements for interim periods. The ASU adds to Topic 270 a principle that requires entities to disclose events since the end of the last annual reporting period that have a material impact on the entity. ASU 2025-11 is effective for interim reporting periods within annual reporting periods beginning after December 15, 2027. The adoption of this standard is not anticipated to have an impact on our results of operations, liquidity, or capital resources.

CODIFICATION IMPROVEMENTS. In December 2025, the FASB issued ASU 2025-12, which makes changes to the Codification that clarify, correct errors, or make minor improvements. The amendments make the Codification easier to understand and apply. The amendments in this ASU are varied in nature and may affect the application of guidance in cases in which the original guidance may have been unclear. ASU 2025-12 is effective for annual reporting periods beginning after December 15, 2026, and interim reporting periods within those annual reporting periods. The adoption of this standard is not anticipated to have an impact on our results of operations, liquidity, or capital resources.

ENVIRONMENTAL CREDITS AND ENVIRONMENTAL CREDIT OBLIGATIONS. In May 2026, the FASB issued ASU 2026-02, which provides recognition, measurement, presentation, and disclosure guidance for environmental credits and related obligations. The guidance is effective for annual periods beginning after December 15, 2027, and interim periods within those annual periods. The ASU is expected to be applicable to the extent the Company generates, purchases, receives, holds, sells, or uses environmental credits, or has regulatory compliance obligations that may be settled using environmental credits. The Company is currently evaluating the impact that the adoption of this standard will have on results of operations, liquidity or capital resources.