Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Sep. 30, 2017
Accumulated other comprehensive income [Roll Forward]
Beginning balance	$ 8,770
Ending balance	8,388
Accumulated other comprehensive income (loss)	(992)	$ (2,030)	$ (1,019)
Foreign currency translation [Member]
Accumulated other comprehensive income [Roll Forward]
Beginning balance	(369)	(812)
Other comprehensive income (loss) before reclassifications	24	(367)
Reclassified to gain/loss on sale of businesses	(17)	266
Ending balance	(362)	(913)
Pension and post retirement [Member]
Accumulated other comprehensive income [Roll Forward]
Beginning balance	(662)	(1,162)
Amortization of deferred actuarial losses into earnings	23	35
Reclassified to gain/loss on sale of businesses	0	20
Ending balance	(639)	(1,107)
Cash Flow Hedges [Member]
Accumulated other comprehensive income [Roll Forward]
Beginning balance	12	(25)
Deferral of gains (losses) arising during the period	1	8
Reclassification of realized (gains) losses to sales and cost of sales	(4)	7
Ending balance	$ 9	$ (10)