- Schedule of Components of Net Periodic Benefit Cost (Income) (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Amortization:
Prior service cost (credit)	$ (4.9)
Net actuarial loss	115.1
Pension Benefits
Components of net periodic benefit cost
Service cost	88.9	$ 97.0	$ 88.0
Interest cost	155.3	151.6	169.5
Expected return on plan assets	(244.8)	(225.2)	(218.3)
Amortization:
Prior service cost (credit)	0.6	(3.7)	(2.9)
Net actuarial loss	113.4	152.9	124.5
Special termination benefit	0.0	0.5	0.5
Settlements	0.7	2.8	0.0
Net periodic benefit cost (income)	114.1	175.9	161.3
Other Postretirement Benefits
Components of net periodic benefit cost
Service cost	1.3	1.4	1.3
Interest cost	2.4	2.5	3.3
Amortization:
Prior service cost (credit)	(5.5)	(6.1)	(11.1)
Net actuarial loss	1.7	2.3	2.3
Special termination benefit	0.0	0.0	0.0
Settlements	0.0	0.0	0.0
Net periodic benefit cost (income)	$ (0.1)	$ 0.1	$ (4.2)