Supplemental Information (Other Noncurrent Liabilities) (Details) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 30, 2016
Supplemental Information [Abstract]
Pension benefits	$ 703.8	$ 1,155.1
Postretirement benefits	57.0	74.9
Other employee benefits	99.3	104.1
Contingencies related to uncertain tax positions	130.6	78.0
Advance payments	39.0	43.8
Environmental liabilities	72.3	70.3
Derivative instruments	36.0	21.8
Asset retirement obligations	144.0	116.1
Obligation for future contribution to an equity affiliate	94.4	94.4
Obligations associated with EfW	65.3	0.0
Other	170.2	58.0
Other noncurrent liabilities	$ 1,611.9	$ 1,816.5