Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Accumulated other comprehensive income [Roll Forward]
Stockholders' equity, Beginning balance	$ 8,273	$ 8,990
Stockholders' equity, Ending balance	8,447	8,273	$ 8,990
Accumulated other comprehensive income (loss)	(1,577)	(1,722)	(1,015)
Foreign currency translation
Accumulated other comprehensive income [Roll Forward]
Stockholders' equity, Beginning balance	(794)	(600)	(369)
Other comprehensive income (loss), net of taxes of $29, $(16) and $0, respectively	83	(194)	(214)
Reclassified to gain/loss on sale of businesses	0	0	(17)
Stockholders' equity, Ending balance	(711)	(794)	(600)
Foreign currency translation, tax	29	(16)	0
Pension and postretirement
Accumulated other comprehensive income [Roll Forward]
Stockholders' equity, Beginning balance	(928)	(420)	(662)
Actuarial gains (losses) deferred during the period, net of taxes of $15, $165, and $(76), respectively	(49)	(560)	250
Amortization of deferred actuarial losses into earnings, net of taxes of $(34), $(15) and $(29), respectively	113	52	94
Stockholders' equity, Ending balance	(864)	(928)	(420)
Actuarial gains (losses) deferred during the period, tax	15	165	(76)
Amortization of deferred actuarial (gains) losses into earnings, tax	(34)	(15)	(29)
Cash flow hedges
Accumulated other comprehensive income [Roll Forward]
Stockholders' equity, Beginning balance	0	5	12
Gains (Losses) deferred during the period, net of taxes of $2, $1 and $0, respectively	(9)	(3)	2
Reclassifications of realized (gains) losses to sales and cost of sales, net of taxes of $(2), $0 and $4, respectively	7	(2)	(11)
Stockholders' equity, Ending balance	(2)	0	5
Gains (losses) deferred during the period, tax	2	1	0
Reclassification of (gains) losses to sales and cost of sales, tax	(2)	0	4
Accounting standards update 2018-02, early adoption [Member] \| Reclassification out of accumulated other comprehensive income [Member] \| Pension and postretirement
Accumulated other comprehensive income [Roll Forward]
Adoption of accounting standard update, accumulated other comprehensive income	0	0	(102)
Accounting standards update 2018-02, early adoption [Member] \| Reclassification out of accumulated other comprehensive income [Member] \| Cash flow hedges
Accumulated other comprehensive income [Roll Forward]
Adoption of accounting standard update, accumulated other comprehensive income	$ 0	$ 0	$ 2

Accumulated other comprehensive income [Roll Forward]

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Amount after tax of increase (decrease) to equity or (increase) decrease to net assets, resulting from the cumulative effect adjustment of a new accounting principle applied in the period of adoption.

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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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