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, 2019	Sep. 30, 2018	Sep. 30, 2017
U.S. Plans
Change in Benefit Obligation
Benefit obligation—beginning of fiscal year	$ 844	$ 913
Service cost	0	0	$ 0
Interest cost	32	32	36
Actuarial loss (gain)	95	(38)
Benefit payments	(52)	(63)
Plan amendment	0	0
Foreign currency exchange rate changes	0	0
Benefit obligation—end of fiscal year	919	844	913
Accumulated benefit obligation	919	844
Change in Plan Assets:
Fair value of plan assets—beginning of fiscal year	1,090	1,074
Actual return on plan assets	52	78
Company contribution	0	1
Benefit payments	(52)	(63)
Foreign currency exchange rate changes	0	0
Fair value of plan assets—end of fiscal year	1,090	1,090	1,074
Funded status at end of fiscal year	171	246
Recognized in Consolidated Balance Sheets:
Non-current asset	178	252
Current liability	(1)	(1)
Non-current liability	(6)	(5)
Funded status at end of fiscal year	171	246
Non-U.S. Plans
Change in Benefit Obligation
Benefit obligation—beginning of fiscal year	452	433
Service cost	4	4	6
Interest cost	13	12	11
Actuarial loss (gain)	109	24
Benefit payments	(22)	(9)
Plan amendment	1	0
Foreign currency exchange rate changes	(29)	(12)
Benefit obligation—end of fiscal year	528	452	433
Accumulated benefit obligation	528	452
Change in Plan Assets:
Fair value of plan assets—beginning of fiscal year	436	433
Actual return on plan assets	93	13
Company contribution	10	11
Benefit payments	(22)	(9)
Foreign currency exchange rate changes	(27)	(12)
Fair value of plan assets—end of fiscal year	490	436	$ 433
Funded status at end of fiscal year	(38)	(16)
Recognized in Consolidated Balance Sheets:
Non-current asset	0	0
Current liability	0	(10)
Non-current liability	(38)	(6)
Funded status at end of fiscal year	$ (38)	$ (16)