Retirement Benefits (Narrative) (Details) - Defined Benefit Pension Plan - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Sep. 30, 2019
Defined Benefit Plan Disclosure [Line Items]
Company contributions	$ 8.3	$ 19.5	$ 40.2
Minimum
Defined Benefit Plan Disclosure [Line Items]
Total expected contributions for current fiscal year	30.0
Maximum
Defined Benefit Plan Disclosure [Line Items]
Total expected contributions for current fiscal year	$ 40.0
International
Defined Benefit Plan Disclosure [Line Items]
Prior service cost arising during period		$ 4.7