Retirement Benefits (Narrative) (Details) - Defined Benefit Pension Plan - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019	Sep. 30, 2019
Defined Benefit Plan Disclosure [Line Items]
Company contributions			$ 14.9	$ 25.5	$ 40.2
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement	$ 1.5
Minimum
Defined Benefit Plan Disclosure [Line Items]
Total expected contributions for current fiscal year	30.0		30.0
Maximum
Defined Benefit Plan Disclosure [Line Items]
Total expected contributions for current fiscal year	40.0		40.0
International
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement	$ 0.0	$ 0.0	$ 0.0	$ (0.2)
Prior service cost arising during period		4.7
U.S. Supplementary Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement		$ 5.0