- Schedule of Components of Net Periodic Benefit Cost (Income) (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Amortization:
Prior service cost (credit)	$ (4.5)
Net actuarial loss	148.7
Pension Benefits
Components of net periodic benefit cost
Service cost	91.1	$ 78.2	$ 88.9
Interest cost	136.4	158.3	155.3
Expected return on plan assets	(244.8)	(244.7)	(244.8)
Amortization:
Prior service cost (credit)	0.9	1.2	0.6
Net actuarial loss	147.3	77.8	113.4
Settlements	0.0	1.2	0.7
Net periodic benefit cost (income)	130.9	72.0	114.1
Other Postretirement Benefits
Components of net periodic benefit cost
Service cost	1.0	0.9	1.3
Interest cost	1.6	2.3	2.4
Amortization:
Prior service cost (credit)	(5.4)	(5.4)	(5.5)
Net actuarial loss	1.4	0.9	1.7
Settlements	0.0	0.0	0.0
Net periodic benefit cost (income)	$ (1.4)	$ (1.3)	$ (0.1)