Investments in Affiliates (Schedule of Summarized Balance Sheet Information for Ibn Sina (National Methanol)) (Details) - National Methanol Company (Ibn Sina) [Member] - USD ($) $ in Millions	Sep. 30, 2018	Sep. 30, 2017
Schedule of summarized balance sheet information for Ibn Sina (National Methanol) [Line Items]
Current assets	$ 448	$ 410
Noncurrent assets	825	833
Current liabilities	200	194
Noncurrent liabilities	$ 450	$ 499

[Line Items] for Schedule of summarized balance sheet information for Ibn Sina (National Methanol) [Table]

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