Retirement Benefits - Components of Net Periodic Benefit Cost (Income) (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2025	Dec. 31, 2024
Pension Benefits
Components of net periodic benefit cost (income)
Service cost	$ 9	$ 10
Interest cost	34	34
Expected return on plan assets	(42)	(41)
Amortization of net actuarial loss	4	6
Net periodic postretirement benefit cost	5	9
Other Postretirement Benefits
Components of net periodic benefit cost (income)
Amortization of net actuarial loss	1	1
Net periodic postretirement benefit cost	$ 1	$ 1