Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Accumulated other comprehensive income [Roll Forward]
Stockholders' equity, Beginning balance	$ 8,990	$ 8,770
Stockholders' equity, Ending balance	8,273	8,990	$ 8,770
Accumulated other comprehensive income (loss)	(1,722)	(1,015)	(1,019)
Foreign currency translation
Accumulated other comprehensive income [Roll Forward]
Stockholders' equity, Beginning balance	(600)	(369)	(812)
Other comprehensive income (loss)	(194)	(214)	58
Reclassified to gain/loss on sale of businesses	0	(17)	385
Stockholders' equity, Ending balance	(794)	(600)	(369)
Foreign currency translation, tax	(16)	0	0
Pension and postretirement
Accumulated other comprehensive income [Roll Forward]
Stockholders' equity, Beginning balance	(420)	(662)	(1,162)
Actuarial gains (losses) deferred during the period	(560)	250	315
Amortization of deferred actuarial losses into earnings	52	94	135
Reclassified to gain/loss on sale of businesses	0	0	50
Stockholders' equity, Ending balance	(928)	(420)	(662)
Actuarial gains (losses) deferred during the period, tax	165	(76)	(170)
Amortization of deferred actuarial (gains) losses into earnings, tax	(15)	(29)	(75)
Cash flow hedges
Accumulated other comprehensive income [Roll Forward]
Stockholders' equity, Beginning balance	5	12	(25)
Gains (Losses) deferred during the period	(3)	2	34
Reclassifications of realized (gains) losses to sales and cost of sales	(2)	(11)	3
Stockholders' equity, Ending balance	0	5	12
Gains (losses) deferred during the period, tax	1	0	(21)
Reclassification of (gains) losses to sales and cost of sales, tax	0	4	(2)
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	(102)	0
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	$ 2	$ 0

Accumulated other comprehensive income [Roll Forward]

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