Business Segment Information - Narrative (Details) $ in Millions	6 Months Ended
	Mar. 31, 2021 USD ($) segment	Sep. 30, 2020 USD ($)
Segment Reporting Information [Line Items]
Number of operating segments | segment	3
Assets	$ 8,317.7	$ 7,264.7
Corporate
Segment Reporting Information [Line Items]
Assets	3,172.7	2,692.0
Corporate | Shared Net Property
Segment Reporting Information [Line Items]
Assets	$ 249.1	$ 247.3