Stockholders' Equity - Narrative (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	1 Months Ended	9 Months Ended	12 Months Ended
	Jun. 30, 2023	Sep. 30, 2023	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021	May 31, 2023	Nov. 15, 2022
Class of Stock [Line Items]
Total cost			$ 1,539.6	$ 142.6	$ 127.0
Remaining authorized repurchase amount		$ 211.5	$ 211.5
Common stock
Class of Stock [Line Items]
Authorized amount for repurchase							$ 1,600.0
Shares repurchased (in shares)		38.9	41.8	4.5	4.8
Total cost		$ 1,431.5	$ 0.5		$ 0.1
Tender Offer
Class of Stock [Line Items]
Shares repurchased (in shares)	27.0
Shares repurchased price (in dollars per share)	$ 38.00
Total cost	$ 1,024.0
Shares repurchased and retired, additional election (in shares)	0.6
Shares repurchased and retired, fees and expenses	$ 16.4
Excise tax recognized	$ 10.2
Tender Offer | Common stock
Class of Stock [Line Items]
Authorized amount for repurchase						$ 1,000.0