Hyperinflationary Economies	12 Months Ended
Sep. 30, 2020
Equity Method Investments And Joint Ventures [Abstract]
Hyperinflationary Economies	Note M. Hyperinflationary Economies Argentina Cabot owns 100% of a carbon black operating entity in Argentina. Beginning on July 1, 2018, the operating entity was considered to be functioning in a highly inflationary economy and began using Cabot’s reporting currency, the U.S. dollar, as its functional currency. There was no financial statement impact at the date of conversion due to the change in functional currency. Since the conversion, all impacts of foreign exchange changes between the reporting currency and Argentine peso are reflected in earnings in the Consolidated Statements of Operations. The Company’s income from operations was not significantly impacted from this change since the operating entity’s sales and a portion of its raw material purchases were already denominated in U.S. dollars. The operating entity’s net revenue represented 2%, 3%, and 2% of Cabot’s total net revenue for fiscal 2020, 2019, and 2018 respectively. The operating entity’s assets and liabilities held in local currency, which consist primarily of cash and cash equivalents, inventories, property, plant and equipment and accounts payable and accrued liabilities, made up less than 2% of Cabot’s total assets and total liabilities at both September 30, 2020, and 2019. Changes in the Argentine peso exchange rate result in foreign currency exchange gains or losses on the operating entity’s peso-denominated monetary assets and liabilities. For fiscal 2020, 2019, and 2018, the Company recorded a net loss of $2 million, net gain of $2 million, and net gain of $3 million, respectively, within Other (income) expense in the Consolidated Statements of Operations, which reflects the remeasurement of the operating entity’s monetary assets and liabilities denominated in Argentine pesos using an exchange rate of 76.12, 57.32, and 39.70 Argentine pesos to the U.S. dollar at September 30, 2020, 2019, and 2018, respectively. Venezuela Cabot owns 49% of a carbon black operating entity in Venezuela, which is accounted for as an equity affiliate, through wholly-owned subsidiaries that carry the investment and receive its dividends. While the operating entity had historically been profitable, it has not been operational in recent periods due to a lack of available raw materials. As such, in fiscal 2019, the Company performed an impairment analysis and determined that the decrease in fair value of the Venezuelan equity investment is other-than-temporary and that the investment is fully impaired. The Company recorded an impairment charge of $11 million in the second quarter of fiscal 2019, which is included in Other income (expense) within the Consolidated Statements of Operations. During the fourth quarter of fiscal 2020, the Venezuela entity was temporarily operational due to availability of raw materials.

Hyperinflationary Economies

12 Months Ended

Sep. 30, 2020

Equity Method Investments And Joint Ventures [Abstract]

Note M. Hyperinflationary Economies

Argentina

Cabot owns 100% of a carbon black operating entity in Argentina. Beginning on July 1, 2018, the operating entity was considered to be functioning in a highly inflationary economy and began using Cabot’s reporting currency, the U.S. dollar, as its functional currency. There was no financial statement impact at the date of conversion due to the change in functional currency. Since the conversion, all impacts of foreign exchange changes between the reporting currency and Argentine peso are reflected in earnings in the Consolidated Statements of Operations.

The Company’s income from operations was not significantly impacted from this change since the operating entity’s sales and a portion of its raw material purchases were already denominated in U.S. dollars. The operating entity’s net revenue represented 2%, 3%, and 2% of Cabot’s total net revenue for fiscal 2020, 2019, and 2018 respectively.

The operating entity’s assets and liabilities held in local currency, which consist primarily of cash and cash equivalents, inventories, property, plant and equipment and accounts payable and accrued liabilities, made up less than 2% of Cabot’s total assets and total liabilities at both September 30, 2020, and 2019. Changes in the Argentine peso exchange rate result in foreign currency exchange gains or losses on the operating entity’s peso-denominated monetary assets and liabilities. For fiscal 2020, 2019, and 2018, the Company recorded a net loss of $2 million, net gain of $2 million, and net gain of $3 million, respectively, within Other

(income) expense in the Consolidated Statements of Operations, which reflects the remeasurement of the operating entity’s monetary assets and liabilities denominated in Argentine pesos using an exchange rate of 76.12, 57.32, and 39.70 Argentine pesos to the U.S. dollar at September 30, 2020, 2019, and 2018, respectively.

Venezuela

Cabot owns 49% of a carbon black operating entity in Venezuela, which is accounted for as an equity affiliate, through wholly-owned subsidiaries that carry the investment and receive its dividends. While the operating entity had historically been profitable, it has not been operational in recent periods due to a lack of available raw materials. As such, in fiscal 2019, the Company performed an impairment analysis and determined that the decrease in fair value of the Venezuelan equity investment is other-than-temporary and that the investment is fully impaired. The Company recorded an impairment charge of $11 million in the second quarter of fiscal 2019, which is included in Other income (expense) within the Consolidated Statements of Operations. During the fourth quarter of fiscal 2020, the Venezuela entity was temporarily operational due to availability of raw materials.