Retirement Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Amortization:
Prior service credit	$ (14.0)
Net actuarial loss	126.8
Pension Benefits [Member]
Components of net periodic benefit cost
Service cost	88.0	$ 85.7	$ 78.5
Interest cost	169.5	167.2	174.2
Expected return on plan assets	(218.3)	(223.2)	(217.9)
Amortization:
Prior service credit	(2.9)	(2.7)	(2.7)
Net actuarial loss	124.5	118.7	99.7
Special termination benefit	0.5	0.0	0.0
Settlements	0.0	0.0	(0.1)
Net periodic benefit cost (income)	161.3	145.7	131.7
Other Postretirement Benefits [Member]
Components of net periodic benefit cost
Service cost	1.3	1.5	2.0
Interest cost	3.3	4.1	6.5
Amortization:
Prior service credit	(11.1)	(14.5)	(10.2)
Net actuarial loss	2.3	4.5	2.9
Special termination benefit	0.0	0.0	0.0
Net periodic benefit cost (income)	$ (4.2)	$ (4.4)	$ 1.2