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Fair Value Measurements - Summary of Investment Portfolio (Parenthetical) (Details) - USD ($) $ in Millions | 6 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2022 | Sep. 30, 2021
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Funds restricted for specific transactions | [1] | $ 44 | $ 91
Environmental Trust [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Funds restricted for specific transactions |  | $ 90 | $ 90
[1] | The March 31, 2022 period included additional contributions to the Environmental trust from proceeds associated with the Performance Adhesives sale and excess land sales. The September 30, 2021 period included $90 million to establish the Environmental trust.

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