Benefit Obligations - Change in Benefit Obligation and Fair Value (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Defined Benefit Plan Disclosure [Line Items]
Curtailment, settlement gain	$ 0	$ 0	$ (9)
Pension Benefits - U.S.
Defined Benefit Plan Disclosure [Line Items]
Curtailment, settlement gain	0	0	2
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation as of beginning of year	3,333	3,174
Service cost	5	5	6
Interest cost	136	145	137
Employee contributions	0	0
Amendments	0	0
Actuarial loss (gain)	205	249
Benefits paid	(235)	(240)
Exchange rate movements	0	0
Curtailments, settlements and other	0	0
Benefit obligation as of end of year	3,444	3,333	3,174
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets as of beginning of year	2,321	2,176
Actual return on plan assets	37	226
Employer contributions	95	160	108
Employee contributions	0	0
Benefits paid	(235)	(240)
Exchange rate movements	0	0
Curtailments, settlements and other	0	(1)
Fair value of plan assets as of end of period	2,218	2,321	2,176
Noncurrent assets	0	0
Accrued benefit liability, current	(7)	(7)
Accrued benefit liability, noncurrent	(1,219)	(1,005)
Net amount recognized	(1,226)	(1,012)
Net prior service cost (credit)	3	4
Net actuarial loss (gain)	1,304	1,054
Net amount recognized	1,307	1,058
Pension Benefits - Non-U.S.
Defined Benefit Plan Disclosure [Line Items]
Curtailment, settlement gain	0	0	0
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation as of beginning of year	616	596
Service cost	7	7	7
Interest cost	15	21	21
Employee contributions	0	0
Amendments	(1)	0
Actuarial loss (gain)	6	57
Benefits paid	(25)	(26)
Exchange rate movements	(67)	(39)
Curtailments, settlements and other	3	0
Benefit obligation as of end of year	554	616	596
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets as of beginning of year	60	51
Actual return on plan assets	6	12
Employer contributions	25	27	25
Employee contributions	0	0
Benefits paid	(25)	(26)
Exchange rate movements	(6)	(4)
Curtailments, settlements and other	(1)	0
Fair value of plan assets as of end of period	59	60	51
Noncurrent assets	1	1
Accrued benefit liability, current	(25)	(27)
Accrued benefit liability, noncurrent	(471)	(530)
Net amount recognized	(495)	(556)
Net prior service cost (credit)	0	0
Net actuarial loss (gain)	136	142
Net amount recognized	136	142
Postretirement Benefits - U.S.
Defined Benefit Plan Disclosure [Line Items]
Curtailment, settlement gain	0	0	(11)
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation as of beginning of year	486	500
Service cost	2	2	3
Interest cost	19	22	20
Employee contributions	13	13
Amendments	(62)	(3)
Actuarial loss (gain)	(14)	14
Benefits paid	(56)	(62)
Exchange rate movements	0	0
Curtailments, settlements and other	0	0
Benefit obligation as of end of year	388	486	500
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets as of beginning of year	173	164
Actual return on plan assets	1	13
Employer contributions	28	45
Employee contributions	13	13
Benefits paid	(56)	(62)
Exchange rate movements	0	0
Curtailments, settlements and other	0	0
Fair value of plan assets as of end of period	159	173	$ 164
Noncurrent assets	0	0
Accrued benefit liability, current	(35)	(40)
Accrued benefit liability, noncurrent	(194)	(273)
Net amount recognized	(229)	(313)
Net prior service cost (credit)	(101)	(52)
Net actuarial loss (gain)	70	81
Net amount recognized	$ (31)	$ 29