Venezuela	12 Months Ended
Sep. 30, 2017
Equity Method Investments And Joint Ventures [Abstract]
Venezuela	Note K. 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 September 30, 2017, these subsidiaries carried the operating affiliate investment of $15 million. During fiscal 2017, 2016 and 2015, the Company received dividends in the amounts of $4 million, $2 million and $6 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 rate made available to the Company as of September 30, 2017 was 3,345 bolivars to the U.S. dollar. The operating affiliate and the Company’s wholly-owned subsidiaries remeasured their bolivar denominated monetary accounts to reflect the current rate. During fiscal 2017, the exchange rate devalued from 656 bolivars to the U.S. dollar to 3,345 bolivars to the U.S. dollar. The impact of the exchange rate devaluations on the operating affiliate’s results was a net gain of $1 million during fiscal 2017. 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.

Venezuela

12 Months Ended

Sep. 30, 2017

Equity Method Investments And Joint Ventures [Abstract]

Note K. 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 September 30, 2017, these subsidiaries carried the operating affiliate investment of $15 million.

During fiscal 2017, 2016 and 2015, the Company received dividends in the amounts of $4 million, $2 million and $6 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 rate made available to the Company as of September 30, 2017 was 3,345 bolivars to the U.S. dollar. The operating affiliate and the Company’s wholly-owned subsidiaries remeasured their bolivar denominated monetary accounts to reflect the current rate. During fiscal 2017, the exchange rate devalued from 656 bolivars to the U.S. dollar to 3,345 bolivars to the U.S. dollar. The impact of the exchange rate devaluations on the operating affiliate’s results was a net gain of $1 million during fiscal 2017.

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.