Retirement Benefits (Narrative) (Details) - Defined Benefit Pension Plan - USD ($) $ in Millions	3 Months Ended			6 Months Ended		12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018	Sep. 30, 2018
Defined Benefit Plan Disclosure [Line Items]
Company contributions				$ 25.5	$ 35.9	$ 68.3
Pension settlement loss	$ 5.0
Minimum
Defined Benefit Plan Disclosure [Line Items]
Total expected contributions for current fiscal year	45.0			45.0
Maximum
Defined Benefit Plan Disclosure [Line Items]
Total expected contributions for current fiscal year	65.0			65.0
International
Defined Benefit Plan Disclosure [Line Items]
Pension settlement loss	$ 0.0		$ 0.0	$ 0.2	$ 0.0
Prior service cost arising during period		$ 4.7