Retirement Benefits - Narrative (Details) - USD ($)	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Defined Benefit Plan Disclosure [Line Items]
Expense related to defined contribution savings plans	$ 85,000,000	$ 92,000,000	$ 77,000,000
Defined benefit plan, percentage of benefit obligation relating to domestic plan	69.00%
Recognized prior service credits	$ (1,000,000)
Recognized prior service credits, net of tax	(1,000,000)
Recognized net actuarial losses	(29,000,000)
Recognized net actuarial losses, net of tax	$ (22,000,000)
Defined benefit plan, net periodic benefit cost (credit) excluding service cost, statement of income or comprehensive income [extensible enumeration]	Accumulated Other Comprehensive Income (Loss), Net of Tax
Defined benefit plan, accumulated benefit obligation	$ 2,771,000,000	2,895,000,000
U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Voluntary contribution to U.S. qualified pension plan	70,000,000	0	0
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Voluntary contribution to U.S. qualified pension plan	88,000,000	27,000,000
Recognized net actuarial losses	27,000,000	$ (1,000,000)	$ (2,000,000)
Estimated future payments, during next fiscal year	$ 23,000,000
Pension Benefits | U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Discount rate	5.35%	5.10%	6.10%
Pension Benefits | Non-U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Discount rate	4.07%	3.87%
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Voluntary contribution to U.S. qualified pension plan	$ 10,000,000	$ 9,000,000
Recognized net actuarial losses	2,000,000	$ 1,000,000	$ 0
Estimated future payments, during next fiscal year	$ 6,000,000
Other Postretirement Benefits | U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Discount rate	5.07%	4.91%
Other Postretirement Benefits | Non-U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Discount rate	4.45%	4.45%
Minimum
Defined Benefit Plan Disclosure [Line Items]
Company contribution to defined contribution plan (percentage)	3.00%
Maximum
Defined Benefit Plan Disclosure [Line Items]
Company contribution to defined contribution plan (percentage)	7.00%