Venezuela	9 Months Ended
Jun. 30, 2018
Equity Method Investments And Joint Ventures [Abstract]
Venezuela	O. Venezuela Cabot owns 49% of a carbon black operating affiliate in Venezuela, which is accounted for as an equity affiliate, through wholly-owned subsidiaries that carry the investment and receive its dividends. As of June 30, 2018, these subsidiaries carried the operating affiliate investment of $13 million. During each of the nine month periods ended June 30, 2018 and 2017, the Company received dividends in the amounts of $3 million, which were paid in U.S. dollars. A significant portion of the Company’s operating affiliate’s sales are exports denominated in U.S. dollars. The Venezuelan government mandates that a certain percentage of the dollars collected from these sales be converted into bolivars. The exchange rates made available to the Company as of June 30, 2018 and September 30, 2017 were 96,000 bolivars and 3,345 bolivars to the U.S. dollar, respectively. Due to a reduced level of export sales in recent quarters, this exchange rate devaluation had an immaterial impact on the Company’s results. The operating entity has historically been profitable. The Company continues to closely monitor developments in Venezuela and their potential impact on the recoverability of its equity affiliate investment. Any future change in the exchange rate made available to the Company could cause the Company to change the exchange rate it uses and result in gains or losses on the bolivar-denominated assets held by its operating affiliate and wholly-owned subsidiaries.

O. Venezuela

Cabot owns 49% of a carbon black operating affiliate in Venezuela, which is accounted for as an equity affiliate, through wholly-owned subsidiaries that carry the investment and receive its dividends. As of June 30, 2018, these subsidiaries carried the operating affiliate investment of $13 million.

During each of the nine month periods ended June 30, 2018 and 2017, the Company received dividends in the amounts of $3 million, which were paid in U.S. dollars.

A significant portion of the Company’s operating affiliate’s sales are exports denominated in U.S. dollars. The Venezuelan government mandates that a certain percentage of the dollars collected from these sales be converted into bolivars. The exchange rates made available to the Company as of June 30, 2018 and September 30, 2017 were 96,000 bolivars and 3,345 bolivars to the U.S. dollar, respectively. Due to a reduced level of export sales in recent quarters, this exchange rate devaluation had an immaterial impact on the Company’s results.

The operating entity has historically been profitable. The Company continues to closely monitor developments in Venezuela and their potential impact on the recoverability of its equity affiliate investment. Any future change in the exchange rate made available to the Company could cause the Company to change the exchange rate it uses and result in gains or losses on the bolivar-denominated assets held by its operating affiliate and wholly-owned subsidiaries.