Venezuela	6 Months Ended
Mar. 31, 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 March 31, 2018, these subsidiaries carried the operating affiliate investment of $13 million. During the six months ended March 31, 2018 and 2017, the Company received dividends in the amounts of $3 million and $2 million, respectively, 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 March 31, 2018 and September 30, 2017 were 49,478 bolivars and 3,345 bolivars to the U.S. dollar, respectively. This exchange rate devaluation had an immaterial impact on the Company’s results. The operating entity has generally 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 March 31, 2018, these subsidiaries carried the operating affiliate investment of $13 million.

During the six months ended March 31, 2018 and 2017, the Company received dividends in the amounts of $3 million and $2 million, respectively, 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 March 31, 2018 and September 30, 2017 were 49,478 bolivars and 3,345 bolivars to the U.S. dollar, respectively. This exchange rate devaluation had an immaterial impact on the Company’s results.

The operating entity has generally 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.