Consolidated Statements of Comprehensive Income (Loss) (Unaudited) (Parenthetical) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Statement of Comprehensive Income [Abstract]
Net derivative gains and other costs arising during the period, net of tax expense	$ 5.8	$ 0.5	$ 6.2	$ 1.5
Reclassification of (gains) losses into net income (loss), net of tax (expense)	$ (0.5)	$ 0.0	$ (1.5)	$ 0.0