SIGNIFICANT ACCOUNTING POLICIES (Policies)	6 Months Ended
Jun. 30, 2025
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The Consolidated Financial Statements and Notes to Consolidated Financial Statements are prepared under GAAP. These accounting principles require management to use estimates and assumptions that impact reported amounts of assets, liabilities, revenues and expenses, and the disclosure of contingent assets and liabilities. Actual results may differ from our estimates. We believe the assumptions underlying these financial statements are reasonable. In our opinion, the accompanying unaudited Consolidated Financial Statements include all adjustments, consisting of normal recurring adjustments, necessary to present a fair statement of our financial position as of June 30, 2025, results of operations for the three and six months ended June 30, 2025 and 2024, statement of changes in stockholders' equity for the three and six months ended June 30, 2025 and 2024, and cash flows for the six months ended June 30, 2025 and 2024. The Consolidated Statement of Financial Position as of December 31, 2024 was derived from audited annual financial statements but does not include all disclosures required by GAAP. Financial results for this interim period are not necessarily indicative of results that may be expected for any other interim period or for the year ending December 31, 2025. The Consolidated Financial Statements should be read in conjunction with DT Midstream's Consolidated Financial Statements and Notes to Consolidated Financial Statements included in DT Midstream's 2024 Annual Report on Form 10-K.
Principles of Consolidation	Principles of Consolidation We consolidate all majority-owned subsidiaries and investments in entities in which we have a controlling influence. Non-controlled investments are accounted for using the equity method of accounting when we are able to significantly influence the operating policies of the investee. When we do not influence the operating policies of an investee, the equity investment is measured at fair value, if readily determinable, or if not readily determinable, at cost less impairment, if applicable. We eliminate all intercompany balances and transactions. We evaluate whether an entity is a VIE whenever reconsideration events occur. We consolidate VIEs for which we are the primary beneficiary. When assessing the determination of the primary beneficiary, we consider all relevant facts and circumstances, including: the power, through voting or similar rights, to direct the activities of the VIE that most significantly impact the VIE's economic performance and the obligation to absorb the expected losses and/or the right to receive the expected returns of the VIE. We perform ongoing reassessments of all VIEs to determine if the primary beneficiary status has changed.
Equity Method Investments	Equity Method Investments Non-controlled investments are accounted for using the equity method of accounting when we are able to significantly influence the operating policies of the investee. Under the equity method of accounting, investments are recorded at historical cost as an asset and adjusted for capital contributions, dividends and distributions received, and our share of the investee's earnings or losses, which are recorded as earnings from equity method investees on the Consolidated Statements of Operations. Equity method investments and related activity are included in the Pipeline segment.
Cash and Cash Equivalents	Cash and Cash Equivalents Cash and cash equivalents include cash in banks and highly liquid money market investments with remaining maturities of three months or less, when purchased. Cash equivalents are stated at cost, which approximates fair value.
Financing Receivables	Financing Receivables Financing receivables are primarily composed of trade accounts receivable and notes receivable, which are stated at net realizable value. We regularly monitor the credit quality of our financing receivables by reviewing counterparty credit quality indicators and monitoring for triggering events, such as a credit rating downgrade or bankruptcy. We have three internal grades of credit quality, with internal grade 1 as the lowest risk and internal grade 3 as the highest risk. The related credit quality indicators and risk ratings utilized to develop the internal grades have been updated through June 30, 2025. As of June 30, 2025, the notes receivable — related party of $4 million, which originated prior to 2021, were classified as internal grade 1. There are no notes receivable on nonaccrual status and no past due financing receivables as of June 30, 2025. For trade accounts receivable, the customer allowance for expected credit loss is calculated based on specific review of future collections based on receivable balances generally in excess of 30 days. Existing and future economic conditions, historical loss rates, customer trends and other relevant factors that may affect our ability to collect are also considered. Receivables are written off on a specific identification basis and determined based on the particular circumstances of the associated receivable.
Operation and Maintenance	Operation and Maintenance Operation and maintenance is primarily comprised of costs for labor and employee benefits, outside services, materials, compression, purchased natural gas, operating lease costs, office costs, and other operating and maintenance costs.
Property, Plant, and Equipment	Property, Plant, and Equipment Property is stated at cost and includes construction-related labor, materials, overhead and capitalized interest. Property for FERC-regulated entities includes debt and equity AFUDC. Debt AFUDC represents capitalized interest. Equity AFUDC represents the capitalization of the estimated average cost of equity during FERC-regulated construction projects and is recorded as a credit to allowance for funds used during construction in our Consolidated Statements of Operations. Expenditures for maintenance and repairs are charged to expense when incurred. Property, plant and equipment is depreciated over its estimated useful life using the straight-line method. Regulated assets are accounted for under ASC 980, which in some cases requires that the cost of regulated property retired or sold, plus removal costs, less salvage, be charged to accumulated depreciation. For regulated assets, depreciation studies to assess the estimated useful lives of the asset are typically conducted as part of rate proceedings or tariff filings. Changes in economic lives, if applicable, are implemented prospectively as of the approved effective date. Our regulated properties are depreciated using the straight-line method based on composite depreciation rates applied to functional groups of properties with similar economic lives.
Depreciation and Amortization	Depreciation and Amortization Depreciation and amortization is related to property, plant and equipment and customer relationships and other intangible assets, net, used in our transportation, storage and gathering businesses.
Long-Lived Assets	Long-Lived Assets Long-lived assets are reviewed for impairment whenever events or changes in circumstances indicate the carrying amount of an asset may not be recoverable. If the carrying amount of the asset exceeds the expected undiscounted future cash flows generated by the asset, an impairment loss is recognized resulting in the asset being written down to its estimated fair value. Assets to be disposed of are reported at the lower of the carrying amount or fair value, less costs to sell.
Intangible Assets	Intangible Assets Intangible assets with finite useful lives are amortized on a straight-line basis over the periods benefited.
Goodwill	Goodwill DT Midstream has goodwill resulting from business combinations. For each reporting unit with goodwill, we perform an impairment test annually or whenever events or circumstances indicate that the value of goodwill may be impaired.
Lessor Accounting	Lessor Accounting A lease exists when we have provided other parties with the right to control the use of identified property, plant or equipment, as conveyed through a contract, for a certain time period and consideration received. The right to control is deemed to occur when we have provided other parties with the right to obtain substantially all of the economic benefits of the identified assets and the right to direct the use of such assets. All of our leases are classified as operating leases. Lease income is recognized on a straight-line, ratable basis over the fixed, non-cancelable term of the relevant contract. Lease income is reported in Operating revenues in our Consolidated Statements of Operations.
Recently Issued Pronouncements	Recently Issued Pronouncements In December 2023, the FASB issued ASU No. 2023-09, Income Taxes (Topic 740) - Improvements to Income Tax Disclosures. The amendments improve transparency of income tax disclosure requirements, primarily through enhanced disclosures of rate reconciliation and income taxes paid. The amendments are effective for annual periods beginning after December 15, 2024. As required, the Company will adopt ASU 2023-09 in its Form 10-K for the year ending December 31, 2025. The adoption of this standard is not expected to have a significant impact on our Consolidated Financial Statements. In November 2024, the FASB issued ASU No. 2024-03, Income Statement—Reporting Comprehensive Income—Expense Disaggregation Disclosures (Subtopic 220-40) - Disaggregation of Income Statement Expenses. The amendments require enhanced disclosures of specified costs and expenses included in significant expense captions in the income statement, including purchases of inventory, employee compensation, depreciation, amortization, and other key amounts. The FASB subsequently issued ASU No. 2025-01 in January 2025 to clarify the effective date of ASU No. 2024-03. The amendments are effective for fiscal years beginning after December 15, 2026 and interim reporting periods within annual reporting periods beginning after December 15, 2027. We are currently evaluating the impact of this standard's adoption on our Consolidated Financial Statements.
Fair Value	Significant Accounting Policy – Fair Value A fair value hierarchy has been established that prioritizes the inputs to valuation techniques used to measure fair value in three broad levels. The fair value hierarchy gives the highest priority to quoted prices (unadjusted) in active markets for identical assets or liabilities (Level 1) and the lowest priority to unobservable inputs (Level 3). In some cases, the inputs used to measure fair value might fall in different levels of the fair value hierarchy. All assets and liabilities are required to be classified in their entirety based on the lowest level of input that is significant to the fair value measurement in its entirety. Assessing the significance of a particular input may require judgment considering factors specific to the asset or liability and may affect the valuation of the asset or liability and its placement within the fair value hierarchy. We classify fair value balances based on the fair value hierarchy defined as follows: •Level 1 — Consists of unadjusted quoted prices in active markets for identical assets or liabilities that we have the ability to access as of the reporting date. •Level 2 — Consists of inputs other than quoted prices included within Level 1 that are directly observable for the assets or liabilities or indirectly observable through corroboration with observable market data. •Level 3 — Consists of unobservable inputs for assets or liabilities whose fair value is estimated based on internally developed models or methodologies using inputs that are generally less readily observable and supported by little, if any, market activity at the measurement date. Unobservable inputs are developed based on the best available information and subject to cost-benefit constraints.
Regulation	Significant Accounting Policy – Regulation Guardian, Midwestern and Viking are subject to rate regulation and accounting requirements of the FERC. The regulated operations of each of these subsidiaries have rates that are (i) established by independent, third-party regulators, (ii) set at levels that will recover our costs when considering the demand and competition for our services and (iii) charged to and collectible from our customers. Accordingly, we follow the accounting for regulated operations as defined in ASC 980 for these pipelines, which results in differences in the application of GAAP between our regulated and non-regulated businesses. During the rate-making process, FERC sets the framework for what we can charge to and collect from our customers for our services and establish the manner that our costs are accounted for, including allowing us to defer recognition of certain costs and permitting cost recovery through rates over time as opposed to expensing such costs as incurred. Examples include costs for fuel and losses, contributions in aid of construction, charges for depreciation, gains or losses on disposition of assets and deferral of tax benefits related to changes in tax rates.

SIGNIFICANT ACCOUNTING POLICIES (Policies)

6 Months Ended

Jun. 30, 2025

The Consolidated Financial Statements and Notes to Consolidated Financial Statements are prepared under GAAP.

These accounting principles require management to use estimates and assumptions that impact reported amounts of assets, liabilities, revenues and expenses, and the disclosure of contingent assets and liabilities. Actual results may differ from our estimates. We believe the assumptions underlying these financial statements are reasonable.

In our opinion, the accompanying unaudited Consolidated Financial Statements include all adjustments, consisting of normal recurring adjustments, necessary to present a fair statement of our financial position as of June 30, 2025, results of operations for the three and six months ended June 30, 2025 and 2024, statement of changes in stockholders' equity for the three and six months ended June 30, 2025 and 2024, and cash flows for the six months ended June 30, 2025 and 2024. The Consolidated Statement of Financial Position as of December 31, 2024 was derived from audited annual financial statements but does not include all disclosures required by GAAP. Financial results for this interim period are not necessarily indicative of results that may be expected for any other interim period or for the year ending December 31, 2025. The Consolidated Financial Statements should be read in conjunction with DT Midstream's Consolidated Financial Statements and Notes to Consolidated Financial Statements included in DT Midstream's 2024 Annual Report on Form 10-K.

Principles of Consolidation

We consolidate all majority-owned subsidiaries and investments in entities in which we have a controlling influence. Non-controlled investments are accounted for using the equity method of accounting when we are able to significantly influence the operating policies of the investee. When we do not influence the operating policies of an investee, the equity investment is measured at fair value, if readily determinable, or if not readily determinable, at cost less impairment, if applicable. We eliminate all intercompany balances and transactions.

We evaluate whether an entity is a VIE whenever reconsideration events occur. We consolidate VIEs for which we are the primary beneficiary. When assessing the determination of the primary beneficiary, we consider all relevant facts and circumstances, including: the power, through voting or similar rights, to direct the activities of the VIE that most significantly impact the VIE's economic performance and the obligation to absorb the expected losses and/or the right to receive the expected returns of the VIE. We perform ongoing reassessments of all VIEs to determine if the primary beneficiary status has changed.

Equity Method Investments

Non-controlled investments are accounted for using the equity method of accounting when we are able to significantly influence the operating policies of the investee. Under the equity method of accounting, investments are recorded at historical cost as an asset and adjusted for capital contributions, dividends and distributions received, and our share of the investee's earnings or losses, which are recorded as earnings from equity method investees on the Consolidated Statements of Operations. Equity method investments and related activity are included in the Pipeline segment.

Cash and Cash Equivalents

Cash and cash equivalents include cash in banks and highly liquid money market investments with remaining maturities of three months or less, when purchased. Cash equivalents are stated at cost, which approximates fair value.

Financing Receivables

Financing receivables are primarily composed of trade accounts receivable and notes receivable, which are stated at net realizable value.

We regularly monitor the credit quality of our financing receivables by reviewing counterparty credit quality indicators and monitoring for triggering events, such as a credit rating downgrade or bankruptcy. We have three internal grades of credit quality, with internal grade 1 as the lowest risk and internal grade 3 as the highest risk. The related credit quality indicators and risk ratings utilized to develop the internal grades have been updated through June 30, 2025. As of June 30, 2025, the notes receivable — related party of $4 million, which originated prior to 2021, were classified as internal grade 1. There are no notes receivable on nonaccrual status and no past due financing receivables as of June 30, 2025.

For trade accounts receivable, the customer allowance for expected credit loss is calculated based on specific review of future collections based on receivable balances generally in excess of 30 days. Existing and future economic conditions, historical loss rates, customer trends and other relevant factors that may affect our ability to collect are also considered. Receivables are written off on a specific identification basis and determined based on the particular circumstances of the associated receivable.

Operation and Maintenance

Operation and maintenance is primarily comprised of costs for labor and employee benefits, outside services, materials, compression, purchased natural gas, operating lease costs, office costs, and other operating and maintenance costs.

Property, Plant, and Equipment

Property is stated at cost and includes construction-related labor, materials, overhead and capitalized interest. Property for FERC-regulated entities includes debt and equity AFUDC. Debt AFUDC represents capitalized interest. Equity AFUDC represents the capitalization of the estimated average cost of equity during FERC-regulated construction projects and is recorded as a credit to allowance for funds used during construction in our Consolidated Statements of Operations. Expenditures for maintenance and repairs are charged to expense when incurred. Property, plant and equipment is depreciated over its estimated useful life using the straight-line method.

Regulated assets are accounted for under ASC 980, which in some cases requires that the cost of regulated property retired or sold, plus removal costs, less salvage, be charged to accumulated depreciation. For regulated assets, depreciation studies to assess the estimated useful lives of the asset are typically conducted as part of rate proceedings or tariff filings. Changes in economic lives, if applicable, are implemented prospectively as of the approved effective date. Our regulated properties are depreciated using the straight-line method based on composite depreciation rates applied to functional groups of properties with similar economic lives.

Depreciation and Amortization

Depreciation and amortization is related to property, plant and equipment and customer relationships and other intangible assets, net, used in our transportation, storage and gathering businesses.

Long-Lived Assets

Long-lived assets are reviewed for impairment whenever events or changes in circumstances indicate the carrying amount of an asset may not be recoverable. If the carrying amount of the asset exceeds the expected undiscounted future cash flows generated by the asset, an impairment loss is recognized resulting in the asset being written down to its estimated fair value. Assets to be disposed of are reported at the lower of the carrying amount or fair value, less costs to sell.

Intangible Assets

Intangible assets with finite useful lives are amortized on a straight-line basis over the periods benefited.

Goodwill

DT Midstream has goodwill resulting from business combinations. For each reporting unit with goodwill, we perform an impairment test annually or whenever events or circumstances indicate that the value of goodwill may be impaired.

Lessor Accounting

A lease exists when we have provided other parties with the right to control the use of identified property, plant or equipment, as conveyed through a contract, for a certain time period and consideration received. The right to control is deemed to occur when we have provided other parties with the right to obtain substantially all of the economic benefits of the identified assets and the right to direct the use of such assets. All of our leases are classified as operating leases. Lease income is recognized on a straight-line, ratable basis over the fixed, non-cancelable term of the relevant contract. Lease income is reported in Operating revenues in our Consolidated Statements of Operations.

Recently Issued Pronouncements

In December 2023, the FASB issued ASU No. 2023-09, Income Taxes (Topic 740) - Improvements to Income Tax Disclosures. The amendments improve transparency of income tax disclosure requirements, primarily through enhanced disclosures of rate reconciliation and income taxes paid. The amendments are effective for annual periods beginning after December 15, 2024. As required, the Company will adopt ASU 2023-09 in its Form 10-K for the year ending December 31, 2025. The adoption of this standard is not expected to have a significant impact on our Consolidated Financial Statements.

In November 2024, the FASB issued ASU No. 2024-03, Income Statement—Reporting Comprehensive Income—Expense Disaggregation Disclosures (Subtopic 220-40) - Disaggregation of Income Statement Expenses. The amendments require enhanced disclosures of specified costs and expenses included in significant expense captions in the income statement, including purchases of inventory, employee compensation, depreciation, amortization, and other key amounts. The FASB subsequently issued ASU No. 2025-01 in January 2025 to clarify the effective date of ASU No. 2024-03. The amendments are effective for fiscal years beginning after December 15, 2026 and interim reporting periods within annual reporting periods beginning after December 15, 2027. We are currently evaluating the impact of this standard's adoption on our Consolidated Financial Statements.

Fair Value

Significant Accounting Policy – Fair Value

A fair value hierarchy has been established that prioritizes the inputs to valuation techniques used to measure fair value in three broad levels. The fair value hierarchy gives the highest priority to quoted prices (unadjusted) in active markets for identical assets or liabilities (Level 1) and the lowest priority to unobservable inputs (Level 3). In some cases, the inputs used to measure fair value might fall in different levels of the fair value hierarchy. All assets and liabilities are required to be classified in their entirety based on the lowest level of input that is significant to the fair value measurement in its entirety. Assessing the significance of a particular input may require judgment considering factors specific to the asset or liability and may affect the valuation of the asset or liability and its placement within the fair value hierarchy. We classify fair value balances based on the fair value hierarchy defined as follows:

•Level 1 — Consists of unadjusted quoted prices in active markets for identical assets or liabilities that we have the ability to access as of the reporting date.

•Level 2 — Consists of inputs other than quoted prices included within Level 1 that are directly observable for the assets or liabilities or indirectly observable through corroboration with observable market data.

•Level 3 — Consists of unobservable inputs for assets or liabilities whose fair value is estimated based on internally developed models or methodologies using inputs that are generally less readily observable and supported by little, if any, market activity at the measurement date. Unobservable inputs are developed based on the best available information and subject to cost-benefit constraints.

Regulation

Significant Accounting Policy – Regulation

Guardian, Midwestern and Viking are subject to rate regulation and accounting requirements of the FERC. The regulated operations of each of these subsidiaries have rates that are (i) established by independent, third-party regulators, (ii) set at levels that will recover our costs when considering the demand and competition for our services and (iii) charged to and collectible from our customers. Accordingly, we follow the accounting for regulated operations as defined in ASC 980 for these pipelines, which results in differences in the application of GAAP between our regulated and non-regulated businesses. During the rate-making process, FERC sets the framework for what we can charge to and collect from our customers for our services and establish the manner that our costs are accounted for, including allowing us to defer recognition of certain costs and permitting cost recovery through rates over time as opposed to expensing such costs as incurred. Examples include costs for fuel and losses, contributions in aid of construction, charges for depreciation, gains or losses on disposition of assets and deferral of tax benefits related to changes in tax rates.