Consolidated Statements of Comprehensive Income (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Statement of Comprehensive Income [Abstract]
Net derivative gains (losses) and other costs arising during the period, net of tax expense	$ 1.6	$ (3.7)	$ 9.5
Reclassification of (gains) into net income (loss), net of tax (expense)	$ (1.4)	$ (2.9)	$ (3.8)