Investments in Affiliates (Schedule of Summarized Income Statement Information for Ibn Sina (National Methanol)) (Details) - National Methanol Company (Ibn Sina) [Member] - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Schedule of Summarized Income Statement Financial Information for Ibn Sina (National Methanol) [Line Items]
Revenues	$ 726	$ 913	$ 759
Gross profit	299	396	306
Net income	$ 227	$ 322	$ 256

[Line Items] for Schedule of Summarized Income Statement Financial Information for Ibn Sina (National Methanol) [Table]

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