Pension and Other Postretirement Benefits - Pension Plan Assets (Detail) - USD ($) $ in Millions	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020
U.S. Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	$ 960	$ 1,288	$ 1,142
U.S. Plans | Fair Value, Measurements, Recurring
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	960	1,288
U.S. Plans | Fair Value, Measurements, Recurring | Cash and cash equivalents
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	40	20
U.S. Plans | Fair Value, Measurements, Recurring | Collective investment funds
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	319	548
U.S. Plans | Fair Value, Measurements, Recurring | Corporate debt securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	392	455
U.S. Plans | Fair Value, Measurements, Recurring | U.S. government-sponsored debt securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	22	28
U.S. Plans | Fair Value, Measurements, Recurring | U.S. Treasury securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	101	105
U.S. Plans | Fair Value, Measurements, Recurring | Asset-backed securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	29	31
U.S. Plans | Fair Value, Measurements, Recurring | Equity securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	57	101
U.S. Plans | Fair Value, Measurements, Recurring | Level 1
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	198	226
U.S. Plans | Fair Value, Measurements, Recurring | Level 1 | Cash and cash equivalents
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	40	20
U.S. Plans | Fair Value, Measurements, Recurring | Level 1 | Collective investment funds
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	0	0
U.S. Plans | Fair Value, Measurements, Recurring | Level 1 | Corporate debt securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	0	0
U.S. Plans | Fair Value, Measurements, Recurring | Level 1 | U.S. government-sponsored debt securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	0	0
U.S. Plans | Fair Value, Measurements, Recurring | Level 1 | U.S. Treasury securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	101	105
U.S. Plans | Fair Value, Measurements, Recurring | Level 1 | Asset-backed securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	0	0
U.S. Plans | Fair Value, Measurements, Recurring | Level 1 | Equity securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	57	101
U.S. Plans | Fair Value, Measurements, Recurring | Level 2
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	733	1,031
U.S. Plans | Fair Value, Measurements, Recurring | Level 2 | Cash and cash equivalents
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	0	0
U.S. Plans | Fair Value, Measurements, Recurring | Level 2 | Collective investment funds
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	319	548
U.S. Plans | Fair Value, Measurements, Recurring | Level 2 | Corporate debt securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	392	455
U.S. Plans | Fair Value, Measurements, Recurring | Level 2 | U.S. government-sponsored debt securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	22	28
U.S. Plans | Fair Value, Measurements, Recurring | Level 2 | U.S. Treasury securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	0	0
U.S. Plans | Fair Value, Measurements, Recurring | Level 2 | Asset-backed securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	0	0
U.S. Plans | Fair Value, Measurements, Recurring | Level 2 | Equity securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	0	0
U.S. Plans | Fair Value, Measurements, Recurring | Level 3
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	29	31
U.S. Plans | Fair Value, Measurements, Recurring | Level 3 | Cash and cash equivalents
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	0	0
U.S. Plans | Fair Value, Measurements, Recurring | Level 3 | Collective investment funds
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	0	0
U.S. Plans | Fair Value, Measurements, Recurring | Level 3 | Corporate debt securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	0	0
U.S. Plans | Fair Value, Measurements, Recurring | Level 3 | U.S. government-sponsored debt securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	0	0
U.S. Plans | Fair Value, Measurements, Recurring | Level 3 | U.S. Treasury securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	0	0
U.S. Plans | Fair Value, Measurements, Recurring | Level 3 | Asset-backed securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	29	31
U.S. Plans | Fair Value, Measurements, Recurring | Level 3 | Equity securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	0	0
Non-U.S. Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	327	548	$ 525
Non-U.S. Plans | Fair Value, Measurements, Recurring
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	327	548
Non-U.S. Plans | Fair Value, Measurements, Recurring | Cash and cash equivalents
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	3	18
Non-U.S. Plans | Fair Value, Measurements, Recurring | Corporate debt securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	91	51
Non-U.S. Plans | Fair Value, Measurements, Recurring | Asset-backed securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	45	78
Non-U.S. Plans | Fair Value, Measurements, Recurring | Equity funds
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	13	68
Non-U.S. Plans | Fair Value, Measurements, Recurring | Multi-asset securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	175	333
Non-U.S. Plans | Fair Value, Measurements, Recurring | Level 1
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	3	18
Non-U.S. Plans | Fair Value, Measurements, Recurring | Level 1 | Cash and cash equivalents
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	3	18
Non-U.S. Plans | Fair Value, Measurements, Recurring | Level 1 | Corporate debt securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	0	0
Non-U.S. Plans | Fair Value, Measurements, Recurring | Level 1 | Asset-backed securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	0	0
Non-U.S. Plans | Fair Value, Measurements, Recurring | Level 1 | Equity funds
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	0	0
Non-U.S. Plans | Fair Value, Measurements, Recurring | Level 1 | Multi-asset securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	0	0
Non-U.S. Plans | Fair Value, Measurements, Recurring | Level 2
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	279	452
Non-U.S. Plans | Fair Value, Measurements, Recurring | Level 2 | Cash and cash equivalents
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	0	0
Non-U.S. Plans | Fair Value, Measurements, Recurring | Level 2 | Corporate debt securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	91	51
Non-U.S. Plans | Fair Value, Measurements, Recurring | Level 2 | Asset-backed securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	0	0
Non-U.S. Plans | Fair Value, Measurements, Recurring | Level 2 | Equity funds
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	13	68
Non-U.S. Plans | Fair Value, Measurements, Recurring | Level 2 | Multi-asset securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	175	333
Non-U.S. Plans | Fair Value, Measurements, Recurring | Level 3
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	45	78
Non-U.S. Plans | Fair Value, Measurements, Recurring | Level 3 | Cash and cash equivalents
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	0	0
Non-U.S. Plans | Fair Value, Measurements, Recurring | Level 3 | Corporate debt securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	0	0
Non-U.S. Plans | Fair Value, Measurements, Recurring | Level 3 | Asset-backed securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	45	78
Non-U.S. Plans | Fair Value, Measurements, Recurring | Level 3 | Equity funds
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	0	0
Non-U.S. Plans | Fair Value, Measurements, Recurring | Level 3 | Multi-asset securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	$ 0	$ 0