Stockholders' Equity - Narrative (Details) - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Class of Stock [Line Items]
Total cost	$ 229.0	$ 1,539.6	$ 142.6
Tender Offer
Class of Stock [Line Items]
Shares repurchased (in shares)		27.0
Total cost		$ 1,024.0
Shares repurchased and retired, fees and expenses		16.4
Excise tax recognized		$ 10.2