Benefit Obligations - Other Comprehensive Income (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Defined Benefit Plan Disclosure [Line Items]
Total recognized in other comprehensive loss	$ 218	$ 201	$ (160)
Pension Benefits - U.S.
Defined Benefit Plan Disclosure [Line Items]
Net loss (gain)	347	193
Prior service cost (credit)	0	0
Amortization of prior service cost (credit)	(1)	(1)
Amortization of actuarial gain	(97)	(82)
Total recognized in other comprehensive loss	249	110
Total recognized in net periodic benefit cost and other comprehensive loss	309	175
Pension Benefits - Non-U.S.
Defined Benefit Plan Disclosure [Line Items]
Net loss (gain)	2	49
Prior service cost (credit)	(1)	0
Amortization of prior service cost (credit)	0	0
Amortization of actuarial gain	(7)	(4)
Total recognized in other comprehensive loss	(6)	45
Total recognized in net periodic benefit cost and other comprehensive loss	21	75
Postretirement Benefits - U.S.
Defined Benefit Plan Disclosure [Line Items]
Net loss (gain)	(6)	12
Prior service cost (credit)	(62)	(3)
Amortization of prior service cost (credit)	13	13
Amortization of actuarial gain	(5)	(4)
Total recognized in other comprehensive loss	(60)	18
Total recognized in net periodic benefit cost and other comprehensive loss	$ (57)	$ 22