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, 2019	Sep. 30, 2018
Schedule of summarized balance sheet information for Ibn Sina (National Methanol) [Line Items]
Current assets	$ 253	$ 448
Noncurrent assets	871	825
Current liabilities	148	200
Noncurrent liabilities	$ 433	$ 450

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

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