Pension and Other Postretirement Benefits - Change in Pension Benefit Obligations, Plan Assets, Funded Status and Amounts Recognized in the Consolidated Balance Sheets (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
U.S. Plans
Change in Benefit Obligation
Benefit obligation at beginning of period	$ 919	$ 844
Service cost	0	0	$ 0
Interest cost	28	32	32
Actuarial loss (gain)	37	95
Benefit payments	(64)	(52)
Plan amendment	0	0
Foreign currency exchange rate changes	0	0
Benefit obligation at end of period	920	919	844
Accumulated benefit obligation	920	919
Change in plan assets:
Fair value of plan assets at beginning of period	1,090	1,090
Actual return on plan assets	114	52
Company contribution	2	0
Benefit payments	(64)	(52)
Foreign currency exchange rate changes	0	0
Fair value of plan assets at end of period	1,142	1,090	1,090
Funded status at end of period	222	171
Recognized in consolidated balance sheets:
Non-current asset	229	178
Current liability	(1)	(1)
Non-current liability	(6)	(6)
Funded status at end of period	222	171
Non-U.S. Plans
Change in Benefit Obligation
Benefit obligation at beginning of period	528	452
Service cost	4	4	4
Interest cost	10	13	12
Actuarial loss (gain)	11	109
Benefit payments	(17)	(22)
Plan amendment	0	1
Foreign currency exchange rate changes	27	(29)
Benefit obligation at end of period	563	528	452
Accumulated benefit obligation	563	528
Change in plan assets:
Fair value of plan assets at beginning of period	490	436
Actual return on plan assets	5	93
Company contribution	22	10
Benefit payments	(17)	(22)
Foreign currency exchange rate changes	25	(27)
Fair value of plan assets at end of period	525	490	$ 436
Funded status at end of period	(38)	(38)
Recognized in consolidated balance sheets:
Non-current asset	0	0
Current liability	0	0
Non-current liability	(38)	(38)
Funded status at end of period	$ (38)	$ (38)