Debt - Exchangeable Senior Notes (Details) - Senior Notes - Exchangeable Senior Notes Maturing May 1 2023 - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Sep. 30, 2021	Jun. 30, 2018
Debt Instrument [Line Items]
Aggregate principal amount		$ 1,000.0
Capped call transactions
Debt Instrument [Line Items]
Aggregate cost of capped calls		$ 87.7
Recognized net loss	$ (424.5)

Face (par) amount of debt instrument at time of issuance.

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