Leases - Future Minimum Lease Payments Under Non-cancelable Operating and Finance Leases (Detail) - USD ($) $ in Millions	Sep. 30, 2020	Oct. 01, 2019	Sep. 30, 2019
Operating leases
2021	$ 17
2022	12
2023	11
2024	10
2025	9
2026 and thereafter	67
Total lease payments	126
Less: imputed interest	22
Operating lease liability	$ 104	$ 111
Operating Lease, Liability, Statement of Financial Position [Extensible List]	cbt:AccountsPayableAndAccruedLiabilitiesAndOtherLiabilitiesMember	cbt:AccountsPayableAndAccruedLiabilitiesAndOtherLiabilitiesMember
Finance leases
2021	$ 5
2022	4
2023	4
2024	4
2025	4
2026 and thereafter	19
Total lease payments	40
Less: imputed interest	9
Total	$ 31		$ 12