Parent's Equity - Summary of Parents Equity (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Beginning	$ 594.3	$ 572.2
Net Income	98.8	105.3
Foreign currency translation	(8.8)	0.1
Net transfers to Parent	(133.8)	(91.8)
Ending	550.5	585.8
Net Parent Investment [Member]
Beginning	864.8	833.8
Net Income	98.8	105.3
Foreign currency translation	0.0	0.0
Net transfers to Parent	(133.8)	(91.8)
Ending	829.8	847.3
AOCI Attributable to Parent [Member]
Beginning	(270.5)	(261.6)
Net Income	0.0	0.0
Foreign currency translation	(8.8)	0.1
Net transfers to Parent	0.0	0.0
Ending	$ (279.3)	$ (261.5)