Amounts in Accumulated Other Comprehensive Income Expected to be Recognized as Components of Net Periodic Benefit Cost over Next Fiscal Year (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Postretirement Benefits
Amortization of:
Service cost	$ 1	$ 2	$ 2
Interest cost	6	7	6
Expected return on plan assets	(9)	(10)	(10)
Net actuarial (gain) loss	17	5	(5)
Curtailment gain	0	0	0
Settlement (gain) loss	0	0	0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)	$ 15	$ 4	$ (7)
Discount rate	3.80%	3.70%	3.30%
Expected return on plan assets	5.65%	5.65%	5.60%
Discontinued Operations | Postretirement Benefits
Amortization of:
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)	$ 0	$ (2)	$ 2
Continuing Operations [Member] | Postretirement Benefits
Amortization of:
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)	15	2	(5)
United States | Pension Benefits
Amortization of:
Service cost	8	15	18
Interest cost	108	105	113
Expected return on plan assets	(199)	(229)	(229)
Net actuarial (gain) loss	361	7	(220)
Curtailment gain	0	0	0
Settlement (gain) loss	13	0	(16)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)	$ 291	$ (102)	$ (334)
Discount rate	4.10%	3.80%	3.70%
Expected return on plan assets	7.10%	7.50%	7.50%
Rate of compensation increase	3.50%	3.20%	3.20%
United States | Discontinued Operations | Pension Benefits
Amortization of:
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)	$ (2)	$ (5)	$ 26
United States | Continuing Operations [Member] | Pension Benefits
Amortization of:
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)	289	(107)	(308)
Non-US [Member] | Pension Benefits
Amortization of:
Service cost	22	23	32
Interest cost	54	57	48
Expected return on plan assets	(105)	(114)	(92)
Net actuarial (gain) loss	236	(22)	(195)
Curtailment gain	0	(2)	(19)
Settlement (gain) loss	4	0	(1)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)	$ 211	$ (58)	$ (227)
Discount rate	2.45%	2.40%	1.90%
Expected return on plan assets	5.20%	5.35%	4.60%
Rate of compensation increase	2.95%	2.90%	2.65%
Non-US [Member] | Discontinued Operations | Pension Benefits
Amortization of:
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)	$ 0	$ (7)	$ 7
Non-US [Member] | Continuing Operations [Member] | Pension Benefits
Amortization of:
Service cost	22	23
Interest cost	54	57
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)	$ 211	$ (65)	$ (220)