Business Segment Information - Narrative (Details) $ in Millions	3 Months Ended	9 Months Ended
	Dec. 31, 2020 segment	Jun. 30, 2021 USD ($) segment	Sep. 30, 2020 USD ($)
Segment Reporting Information [Line Items]
Number of operating segments | segment	3	3
Assets		$ 8,573.1	$ 7,264.7
Corporate
Segment Reporting Information [Line Items]
Assets		3,366.1	2,692.0
Corporate | Shared Net Property
Segment Reporting Information [Line Items]
Assets		$ 240.1	$ 247.3