Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017	Sep. 30, 2017
Accumulated other comprehensive income [Roll Forward]
Beginning balance			$ 8,770
Ending balance	$ 8,537		8,537
Accumulated other comprehensive income (loss)	(827)	$ (1,690)	(827)	$ (1,690)	$ (1,019)
Foreign currency translation [Member]
Accumulated other comprehensive income [Roll Forward]
Beginning balance	(362)	(913)	(369)	(812)
Other comprehensive income (loss) before reclassifications	148	139	172	(228)
Reclassified to gain/loss on sale of businesses	0	119	(17)	385
Ending balance	(214)	(655)	(214)	(655)
Pension and post retirement [Member]
Accumulated other comprehensive income [Roll Forward]
Beginning balance	(639)	(1,107)	(662)	(1,162)
Amortization of deferred actuarial losses into earnings	22	35	45	70
Reclassified to gain/loss on sale of businesses	0	30	0	50
Ending balance	(617)	(1,042)	(617)	(1,042)
Cash Flow Hedges [Member]
Accumulated other comprehensive income [Roll Forward]
Beginning balance	9	(10)	12	(25)
Deferral of gains (losses) arising during the period	(1)	15	0	23
Reclassification of realized (gains) losses to sales and cost of sales	(4)	2	(8)	9
Ending balance	$ 4	$ 7	$ 4	$ 7