Commitments and Contingencies (Tables)

9 Months Ended

Jun. 30, 2017

Commitments And Contingencies Disclosure [Abstract]

Schedule of Components of Purchase Commitments

Cabot has entered into long-term purchase agreements primarily for the purchase of raw materials. Under certain of these agreements the quantity of material being purchased is fixed, but the price paid changes as market prices change. For those commitments, the amounts included in the table below are based on market prices at June 30, 2017.

	Payments Due by Fiscal Year
	Remainder of Fiscal 2017		2018		2019		2020		2021		Thereafter		Total
	(In millions)
Reinforcement Materials	$	59	$	213	$	209	$	135	$	102	$	1,458	$	2,176
Performance Chemicals		10		36		35		30		28		201		340
Purification Solutions		3		9		7		6		—		—		25
Total	$	72	$	258	$	251	$	171	$	130	$	1,659	$	2,541