Retirement Benefits (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017	Mar. 31, 2016
Pension Benefits [Member]
Components of net periodic benefit cost (income)
Service cost	$ 24.2	$ 21.8	$ 48.3	$ 43.9
Interest cost	37.8	42.2	75.6	84.7
Expected return on plan assets	(56.2)	(54.4)	(112.4)	(109.1)
Amortization:
Prior service credit	(1.1)	(0.7)	(1.9)	(1.4)
Net actuarial loss	38.2	31.1	76.2	62.2
Settlements	0.0	0.0	0.2	0.0
Net periodic benefit cost (income)	42.9	40.0	86.0	80.3
Other Postretirement Benefits [Member]
Components of net periodic benefit cost (income)
Service cost	0.4	0.3	0.7	0.6
Interest cost	0.7	0.9	1.3	1.7
Amortization:
Prior service credit	(1.5)	(2.9)	(3.0)	(5.7)
Net actuarial loss	0.6	0.7	1.1	1.3
Net periodic benefit cost (income)	$ 0.2	$ (1.0)	$ 0.1	$ (2.1)