Retirement Benefits (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015	Mar. 31, 2014
Pension Benefits [Member]
Components of net periodic benefit cost
Service cost	$ 21.5	$ 19.6	$ 43.2	$ 39.3
Interest cost	41.6	43.6	83.9	87.2
Expected return on plan assets	(55.8)	(54.5)	(111.9)	(109.0)
Amortization:
Prior service credit	(0.6)	(0.7)	(1.3)	(1.4)
Net actuarial loss	29.6	24.9	59.6	49.8
Net periodic benefit cost	36.3	32.9	73.5	65.9
Other Postretirement Benefits [Member]
Components of net periodic benefit cost
Service cost	0.4	0.5	0.8	1.0
Interest cost	1.1	1.6	2.1	3.2
Amortization:
Prior service credit	(3.7)	(2.7)	(7.4)	(5.2)
Net actuarial loss	1.1	0.9	2.3	1.6
Net periodic benefit cost	$ (1.1)	$ 0.3	$ (2.2)	$ 0.6