Significant Accounting Policies	9 Months Ended
Jun. 30, 2025
Accounting Policies [Abstract]
Significant Accounting Policies	B. Significant Accounting Policies Full detail on the Company’s significant accounting policies may be obtained by referring to Note A in the 2024 10-K. Argentinian Government Actions The Company’s wholly-owned Argentinian subsidiary operates in a highly inflationary economy and, as a result, the functional currency of the subsidiary is Cabot’s reporting currency, the U.S. dollar. During the three and nine months ended June 30, 2025, the Company recorded foreign exchange losses of $3 million and $5 million, respectively, related to the revaluation of non-functional currency denominated monetary asset and liability balances. During the three and nine months ended June 30, 2024, the Company recorded foreign exchange losses of $2 million and $42 million, respectively, related to the revaluation of non-functional currency denominated monetary asset and liability balances. Of the $42 million of foreign exchange losses in the nine months ended June 30, 2024, $33 million related to a single devaluation action in December 2023 by the Argentine government. The Company invests cash in money market funds and recorded investment income of $1 million and $2 million for the three and nine months ended June 30, 2025, respectively, and nil and $16 million, respectively, for the three and nine months ended June 30, 2024. The foreign exchange losses and investment gains are recorded in Other income (expense) in the Consolidated Statement of Operations. During the three months ended March 31, 2024, the Company purchased $30 million in BOPREAL bonds (standing for “Bond for the Reconstruction of a Free Argentina” in Spanish), which are U.S. dollar-denominated securities issued by the Central Bank of Argentina, as part of an Argentine government program to settle foreign payables for importers with debts for goods with customs registration and/or services, incurred on or prior to December 12, 2023. The Company subsequently sold the bonds for $22 million and utilized the proceeds to partially repay its foreign payables in Argentina. The purchase and proceeds of BOPREAL bonds are included in the Changes in Prepaid expenses and other assets in the Consolidated Statement of Cash Flows. The $8 million investment loss is included in Other non-cash (income) expense in the Consolidated Statement of Cash Flows and in Other income (expense) in the Consolidated Statement of Operations. In accordance with Argentine government regulations, the Company purchased an additional $8 million of U.S. dollars in the third quarter of fiscal 2024 at a foreign exchange loss of $2 million and utilized the funds to complete the settlement of outstanding foreign payables incurred on or prior to December 12, 2023. Payables incurred after December 12, 2023 are not subject to payment through the BOPREAL bond program and the Company has settled these payables through regular operations. As such, there has been no BOPREAL bond activity in fiscal 2025. Recent Accounting Pronouncements and Tax Legislation On July 4, 2025, the U.S. federal government enacted the One Big Beautiful Bill Act (“OBBBA”). The OBBBA contains significant changes to federal tax law, such as the permanent extension of certain expiring provisions of the Tax Cuts and Jobs Act, modifications to the international tax framework and the restoration of favorable tax treatment for certain business provisions, and numerous effective dates, all of which the Company is evaluating. The Company expects to complete its evaluation of the impact of the OBBBA on the realizability of the Company’s U.S. net deferred tax assets to reflect the results of this assessment in the Company’s Consolidated Financial Statements for its fiscal year ending September 30, 2025. In November 2024, the FASB issued a new standard, Expense Disaggregation Disclosures. The new guidance requires quantitative and qualitative disclosure of certain cost and expense categories in the notes to the financial statements for interim and annual reporting periods. The new standard is effective for the Company's fiscal years and interim periods beginning October 1, 2027, with early adoption permitted. The Company is currently evaluating the timing of adoption and evaluating the impact of the potential adoption of this standard on the Company’s Consolidated Financial Statements. In December 2023, the FASB issued a new standard, Improvements to Income Tax Disclosures. The new guidance requires additional disclosures primarily related to the income tax rate reconciliation and income taxes paid. The new standard is effective for the Company’s fiscal years and interim periods beginning October 1, 2025. The Company is currently evaluating the impact of the adoption of this standard on the Company's Consolidated Financial Statements. In November 2023, the FASB issued a new standard, Improvement to Reportable Segment Disclosures. The new guidance requires enhanced disclosure of significant reportable segment expenses. The new standard is effective for the Company’s current fiscal year which began October 1, 2024, and for interim periods beginning October 1, 2025. The Company is currently evaluating the impact of the adoption of this standard on the Company’s Consolidated Financial Statements.

Significant Accounting Policies

9 Months Ended

Jun. 30, 2025

B. Significant Accounting Policies

Full detail on the Company’s significant accounting policies may be obtained by referring to Note A in the 2024 10-K.

Argentinian Government Actions

The Company’s wholly-owned Argentinian subsidiary operates in a highly inflationary economy and, as a result, the functional currency of the subsidiary is Cabot’s reporting currency, the U.S. dollar. During the three and nine months ended June 30, 2025, the Company recorded foreign exchange losses of $3 million and $5 million, respectively, related to the revaluation of non-functional currency denominated monetary asset and liability balances. During the three and nine months ended June 30, 2024, the Company recorded foreign exchange losses of $2 million and $42 million, respectively, related to the revaluation of non-functional currency denominated monetary asset and liability balances. Of the $42 million of foreign exchange losses in the nine months ended June 30, 2024, $33 million related to a single devaluation action in December 2023 by the Argentine government. The Company invests cash in money market funds and recorded investment income of $1 million and $2 million for the three and nine months ended June 30, 2025, respectively, and nil and $16 million, respectively, for the three and nine months ended June 30, 2024. The foreign exchange losses and investment gains are recorded in Other income (expense) in the Consolidated Statement of Operations.

During the three months ended March 31, 2024, the Company purchased $30 million in BOPREAL bonds (standing for “Bond for the Reconstruction of a Free Argentina” in Spanish), which are U.S. dollar-denominated securities issued by the Central Bank of Argentina, as part of an Argentine government program to settle foreign payables for importers with debts for goods with customs registration and/or services, incurred on or prior to December 12, 2023. The Company subsequently sold the bonds for $22 million and utilized the proceeds to partially repay its foreign payables in Argentina. The purchase and proceeds of BOPREAL bonds are included in the Changes in Prepaid expenses and other assets in the Consolidated Statement of Cash Flows. The $8 million investment loss is included in Other non-cash (income) expense in the Consolidated Statement of Cash Flows and in Other income (expense) in the Consolidated Statement of Operations. In accordance with Argentine government regulations, the Company purchased an additional $8 million of U.S. dollars in the third quarter of fiscal 2024 at a foreign exchange loss of $2 million and utilized the funds to complete the settlement of outstanding foreign payables incurred on or prior to December 12, 2023. Payables incurred after December 12, 2023 are not subject to payment through the BOPREAL bond program and the Company has settled these payables through regular operations. As such, there has been no BOPREAL bond activity in fiscal 2025.

Recent Accounting Pronouncements and Tax Legislation

On July 4, 2025, the U.S. federal government enacted the One Big Beautiful Bill Act (“OBBBA”). The OBBBA contains significant changes to federal tax law, such as the permanent extension of certain expiring provisions of the Tax Cuts and Jobs Act, modifications to the international tax framework and the restoration of favorable tax treatment for certain business provisions, and numerous effective dates, all of which the Company is evaluating. The Company expects to complete its evaluation of the impact of the OBBBA on the realizability of the Company’s U.S. net deferred tax assets to reflect the results of this assessment in the Company’s Consolidated Financial Statements for its fiscal year ending September 30, 2025.

In November 2024, the FASB issued a new standard, Expense Disaggregation Disclosures. The new guidance requires quantitative and qualitative disclosure of certain cost and expense categories in the notes to the financial statements for interim and annual reporting periods. The new standard is effective for the Company's fiscal years and interim periods beginning October 1, 2027, with early adoption permitted. The Company is currently evaluating the timing of adoption and evaluating the impact of the potential adoption of this standard on the Company’s Consolidated Financial Statements.

In December 2023, the FASB issued a new standard, Improvements to Income Tax Disclosures. The new guidance requires additional disclosures primarily related to the income tax rate reconciliation and income taxes paid. The new standard is effective for the Company’s fiscal years and interim periods beginning October 1, 2025. The Company is currently evaluating the impact of the adoption of this standard on the Company's Consolidated Financial Statements.

In November 2023, the FASB issued a new standard, Improvement to Reportable Segment Disclosures. The new guidance requires enhanced disclosure of significant reportable segment expenses. The new standard is effective for the Company’s current fiscal year which began October 1, 2024, and for interim periods beginning October 1, 2025. The Company is currently evaluating the impact of the adoption of this standard on the Company’s Consolidated Financial Statements.