Stockholders' Equity - Share Repurchase (Details) shares in Millions, $ in Millions	3 Months Ended	6 Months Ended
	Mar. 31, 2024 USD ($) shares	Mar. 31, 2024 USD ($) shares
Stockholders' Equity Note [Abstract]
Stock repurchased and retired during period, shares (in shares) | shares	1.2	3.5
Payments for repurchase of common stock, excluding fees, commissions, and excise tax	$ 73.9	$ 186.8
Exercise tax related to share repurchases	$ 1.7	$ 1.7