Commitments and Contingencies (Tables)

9 Months Ended

Jun. 30, 2018

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 these purchase commitments, the amounts included in the table below are based on market prices at June 30, 2018, which may differ from actual market prices at the time of purchase.

	Payments Due by Fiscal Year
	Remainder of Fiscal 2018		2019		2020		2021		2022		Thereafter		Total
	(In millions)
Reinforcement Materials	$	79	$	294	$	180	$	140	$	140	$	1,901	$	2,734
Performance Chemicals		19		67		55		54		54		461		710
Purification Solutions		3		7		6		1		—		—		17
Specialty Fluids		—		15		—		—		—		—		15
Total	$	101	$	383	$	241	$	195	$	194	$	2,362	$	3,476