Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019	Sep. 30, 2019
Accumulated other comprehensive income [Roll Forward]
Beginning balance			$ 8,273
Ending balance	$ 7,563	$ 8,572	7,563	$ 8,572
Accumulated other comprehensive income (loss)	(1,903)	(928)	(1,903)	(928)	$ (1,722)
Foreign currency translation [Member]
Accumulated other comprehensive income [Roll Forward]
Beginning balance	(695)	(635)	(794)	(600)
Other comprehensive income (loss), foreign currency translation, net of tax of $(13), $(1), $(7), and $(1)	(282)	87	(183)	52
Ending balance	(977)	(548)	(977)	(548)
Pension and post retirement [Member]
Accumulated other comprehensive income [Roll Forward]
Beginning balance	(900)	(407)	(928)	(420)
Amortization of deferred actuarial losses into earnings, net of tax of $(8), $(4), $(17) and $(8)	30	12	58	25
Ending balance	(870)	(395)	(870)	(395)
Cash Flow Hedges [Member]
Accumulated other comprehensive income [Roll Forward]
Beginning balance	19	(10)	0	5
Deferral of gains (losses) arising during the period, net of tax of $23, $(8), $17 and $(3)	(74)	24	(53)	10
Reclassification of realized gains (losses) to sales and cost of sales, net of tax of $1, $0, $1 and $0	(1)	1	(3)	0
Ending balance	$ (56)	$ 15	$ (56)	$ 15

Accumulated other comprehensive income [Roll Forward]

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Accumulated change in equity from transactions and other events and circumstances from non-owner sources, net of tax effect, at period end. Excludes Net Income (Loss), and accumulated changes in equity from transactions resulting from investments by owners and distributions to owners. Includes foreign currency translation items, certain pension adjustments, unrealized gains and losses on certain investments in debt and equity securities, other than temporary impairment (OTTI) losses related to factors other than credit losses on available-for-sale and held-to-maturity debt securities that an entity does not intend to sell and it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis, as well as changes in the fair value of derivatives related to the effective portion of a designated cash flow hedge.

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Amount after tax and reclassification adjustments of gain (loss) on foreign currency translation adjustments, foreign currency transactions designated and effective as economic hedges of a net investment in a foreign entity and intra-entity foreign currency transactions that are of a long-term-investment nature, attributable to parent entity.

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Amount, after tax and reclassification adjustment, of (increase) decrease in accumulated other comprehensive income for defined benefit plan.

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Amount after tax of reclassification adjustment from accumulated other comprehensive income of accumulated gain (loss) realized from derivative instruments designated and qualifying as the effective portion of cash flow hedges and an entity's share of an equity investee's deferred hedging gain (loss).

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Amount of stockholders' equity (deficit), net of receivables from officers, directors, owners, and affiliates of the entity, attributable to both the parent and noncontrolling interests. Amount excludes temporary equity. Alternate caption for the concept is permanent equity.

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