- Schedule of Components of Net Periodic Benefit Cost (Income) (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Amortization:
Prior service cost (credit)	$ (4.2)
Net actuarial loss	78.7
Pension Benefits
Components of net periodic benefit cost
Service cost	78.2	$ 88.9	$ 97.0
Interest cost	158.3	155.3	151.6
Expected return on plan assets	(244.7)	(244.8)	(225.2)
Amortization:
Prior service cost (credit)	1.2	0.6	(3.7)
Net actuarial loss	77.8	113.4	152.9
Settlements	1.2	0.7	3.3
Net periodic benefit cost (income)	72.0	114.1	175.9
Other Postretirement Benefits
Components of net periodic benefit cost
Service cost	0.9	1.3	1.4
Interest cost	2.3	2.4	2.5
Amortization:
Prior service cost (credit)	(5.4)	(5.5)	(6.1)
Net actuarial loss	0.9	1.7	2.3
Settlements	0.0	0.0	0.0
Net periodic benefit cost (income)	$ (1.3)	$ (0.1)	$ 0.1