Retirement Benefits (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Pension Benefits [Member]
Components of net periodic benefit cost (income)
Service cost	$ 24.1	$ 22.1
Interest cost	37.8	42.5
Expected return on plan assets	(56.2)	(54.7)
Amortization:
Prior service credit	(0.8)	(0.7)
Net actuarial loss	38.0	31.1
Settlements	0.2	0.0
Net periodic benefit cost (income)	43.1	40.3
Other Postretirement Benefits [Member]
Components of net periodic benefit cost (income)
Service cost	0.3	0.3
Interest cost	0.6	0.8
Amortization:
Prior service credit	(1.5)	(2.8)
Net actuarial loss	0.5	0.6
Net periodic benefit cost (income)	(0.1)	(1.1)
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Amortization:
Settlements	$ 0.2	$ 0.0