Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Accumulated other comprehensive income [Roll Forward]
Stockholders' equity, Beginning balance	$ 8,770	$ 7,618
Stockholders' equity, Ending balance	8,990	8,770	$ 7,618
Accumulated other comprehensive income (loss)	(1,015)	(1,019)	(1,999)
Foreign currency translation
Accumulated other comprehensive income [Roll Forward]
Stockholders' equity, Beginning balance	(369)	(812)	(622)
Other comprehensive income (loss)	(214)	58	(190)
Reclassified to gain/loss on sale of businesses	(17)	385	0
Stockholders' equity, Ending balance	(600)	(369)	(812)
Pension and postretirement
Accumulated other comprehensive income [Roll Forward]
Stockholders' equity, Beginning balance	(662)	(1,162)	(952)
Actuarial gains (losses) deferred during the period	250	315	(310)
Amortization of deferred actuarial losses into earnings	94	135	100
Reclassified to gain/loss on sale of businesses	0	50	0
Stockholders' equity, Ending balance	(420)	(662)	(1,162)
Actuarial gains (losses) deferred during the period, tax	(76)	(170)	159
Amortization of deferred actuarial (gains) losses into earnings, tax	(29)	(75)	(59)
Cash flow hedges
Accumulated other comprehensive income [Roll Forward]
Stockholders' equity, Beginning balance	12	(25)	(43)
Gains (Losses) deferred during the period	2	34	(30)
Reclassifications of realized (gains) losses to sales and cost of sales	(11)	3	48
Stockholders' equity, Ending balance	5	12	(25)
Gains (losses) deferred during the period, tax	0	(21)	17
Reclassification of (gains) losses to sales and cost of sales, tax	4	(2)	(28)
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	(102)	0	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	$ 2	$ 0	$ 0