Supplemental Information (Other Non-Operating Income (Expense), Net) (Details) - USD ($) $ in Millions		3 Months Ended	12 Months Ended
		Sep. 30, 2018	Sep. 30, 2018		Sep. 30, 2017		Sep. 30, 2016
Supplemental Information [Abstract]
Interest income	[1]		$ 46.3		$ 29.8		$ 0.0
Pension settlement loss		$ (43.7)	(48.5)	[2]	(10.5)	[2]	(5.1)	[2]
Other non-service pension benefit (costs)			7.7		(1.9)		(0.3)
Other			(0.4)		(0.8)		0.0
Other non-operating income (expense), net			$ 5.1		$ 16.6		$ (5.4)

[1] Prior to the second quarter of fiscal year 2017, interest income associated with our cash and cash items and short-term investments was reflected on the consolidated income statements in "Other income (expense), net."

[2] Fiscal year 2018 includes a loss of $43.7 that primarily resulted from the transfer of certain pension payment obligations to an insurer through the purchase of an irrevocable, nonparticipating group annuity contract during the fourth quarter.