Retirement Benefits (Tables)

6 Months Ended

Mar. 31, 2024

Retirement Benefits [Abstract]

Schedule of Net Benefit Costs

The components of net periodic pension and postretirement benefit cost were (in millions):

	Pension Benefits
	Three Months Ended March 31,				Six Months Ended March 31,
	2024		2023		2024		2023
Service cost	$	9.2	$	10.6	$	18.5	$	21.2
Interest cost	36.7		39.5		73.3		78.7
Expected return on plan assets	(42.5)		(51.7)		(84.7)		(103.0)
Amortization of net actuarial gain	(0.2)		(1.0)		(0.5)		(2.0)
Settlement charge	—		117.9		—		117.9
Net periodic pension benefit cost	$	3.2	$	115.3	$	6.6	$	112.8

	Other Postretirement Benefits
	Three Months Ended March 31,				Six Months Ended March 31,
	2024		2023		2024		2023
Service cost	$	0.2	$	0.1	$	0.3	$	0.2
Interest cost	0.7		0.5		1.3		1.1
Amortization of net actuarial loss	0.4		0.2		0.8		0.3
Net periodic postretirement benefit cost	$	1.3	$	0.8	$	2.4	$	1.6