Plan's Investments at Fair Value (Detail) - USD ($) $ in Millions		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value, assets, level 1 to level 2 transfers, amount		$ 0
Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value, assets, level 1 to level 2 transfers, amount		0	$ 0
U.S. Plans | Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		$ 1,074	1,077	$ 1,022
U.S. Plans | Fixed income securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Actual plan asset allocations		33.00%
U.S. Plans | Other security investments
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Actual plan asset allocations		3.00%
U.S. Plans | Equity securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Actual plan asset allocations		64.00%
U.S. Plans | Fair Value, Measurements, Recurring | Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		$ 1,074	1,077
U.S. Plans | Fair Value, Measurements, Recurring | Cash equivalents | Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		31	39
U.S. Plans | Fair Value, Measurements, Recurring | Collective investment funds | Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		540	0
U.S. Plans | Fair Value, Measurements, Recurring | Corporate debt securities | Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		197	185
U.S. Plans | Fair Value, Measurements, Recurring | U.S. government-sponsored debt securities | Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		47	30
U.S. Plans | Fair Value, Measurements, Recurring | U.S. Treasury securities | Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		75	100
U.S. Plans | Fair Value, Measurements, Recurring | Asset-backed securities | Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		39	51
U.S. Plans | Fair Value, Measurements, Recurring | Equity securities | Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		145	672
U.S. Plans | Fair Value, Measurements, Recurring | Level 1 | Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		251	811
U.S. Plans | Fair Value, Measurements, Recurring | Level 1 | Cash equivalents | Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		31	39
U.S. Plans | Fair Value, Measurements, Recurring | Level 1 | U.S. Treasury securities | Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		75	100
U.S. Plans | Fair Value, Measurements, Recurring | Level 1 | Equity securities | Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		145	672
U.S. Plans | Fair Value, Measurements, Recurring | Level 2 | Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		784	215
U.S. Plans | Fair Value, Measurements, Recurring | Level 2 | Collective investment funds | Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		540	0
U.S. Plans | Fair Value, Measurements, Recurring | Level 2 | Corporate debt securities | Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		197	185
U.S. Plans | Fair Value, Measurements, Recurring | Level 2 | U.S. government-sponsored debt securities | Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		47	30
U.S. Plans | Fair Value, Measurements, Recurring | Level 3 | Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		39	51
U.S. Plans | Fair Value, Measurements, Recurring | Level 3 | Asset-backed securities | Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		39	51
Non-U.S. Plans | Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		$ 433	415	$ 0
Non-U.S. Plans | Fixed income securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target allocation, percentage		47.00%
Actual plan asset allocations		44.00%
Non-U.S. Plans | Other security investments
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target allocation, percentage		25.00%
Actual plan asset allocations		25.00%
Non-U.S. Plans | Equity securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target allocation, percentage		28.00%
Actual plan asset allocations		31.00%
Non-U.S. Plans | Fair Value, Measurements, Recurring | Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		$ 433	415
Non-U.S. Plans | Fair Value, Measurements, Recurring | Cash equivalents | Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		1	105
Non-U.S. Plans | Fair Value, Measurements, Recurring | Corporate debt securities | Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		39	39
Non-U.S. Plans | Fair Value, Measurements, Recurring | UK Treasury securities | Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		150	52
Non-U.S. Plans | Fair Value, Measurements, Recurring | Asset-backed securities | Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		32	29
Non-U.S. Plans | Fair Value, Measurements, Recurring | Equity securities | Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		134	116
Non-U.S. Plans | Fair Value, Measurements, Recurring | Multi-asset securities | Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	[1]	77	74
Non-U.S. Plans | Fair Value, Measurements, Recurring | Level 1 | Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		285	273
Non-U.S. Plans | Fair Value, Measurements, Recurring | Level 1 | Cash equivalents | Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		1	105
Non-U.S. Plans | Fair Value, Measurements, Recurring | Level 1 | UK Treasury securities | Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		150	52
Non-U.S. Plans | Fair Value, Measurements, Recurring | Level 1 | Equity securities | Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		134	116
Non-U.S. Plans | Fair Value, Measurements, Recurring | Level 2 | Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		116	113
Non-U.S. Plans | Fair Value, Measurements, Recurring | Level 2 | Corporate debt securities | Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		39	39
Non-U.S. Plans | Fair Value, Measurements, Recurring | Level 2 | Multi-asset securities | Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	[1]	77	74
Non-U.S. Plans | Fair Value, Measurements, Recurring | Level 3 | Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		32	29
Non-U.S. Plans | Fair Value, Measurements, Recurring | Level 3 | Asset-backed securities | Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		$ 32	$ 29
Minimum | U.S. Plans | Fixed income securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target allocation, percentage		25.00%
Minimum | U.S. Plans | Equity securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target allocation, percentage		50.00%
Maximum | U.S. Plans | Fixed income securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target allocation, percentage		35.00%
Maximum | U.S. Plans | Other security investments
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target allocation, percentage		7.00%
Maximum | U.S. Plans | Equity securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target allocation, percentage		80.00%

[1] Multi-asset securities represent pension plan assets that are invested in funds comprised of broad ranges of assets.