Intangible Assets - Gross and Net Intangible Assets by Major Class (Details) - USD ($) $ in Millions	Sep. 30, 2022	Sep. 30, 2021
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross amount	$ 61.5	$ 72.8
Finite-lived intangible assets, accumulated amortization	(39.0)	(35.9)
Finite-lived intangible assets, net amount	22.5	36.9
Indefinite-lived intangible assets	5.5	5.8
Intangible assets, gross amount	67.0	78.6
Total intangible assets, net amount	28.0	42.7
Website domains
Acquired Finite-Lived Intangible Assets [Line Items]
Indefinite-lived license agreements	1.8	2.1
Business licenses
Acquired Finite-Lived Intangible Assets [Line Items]
Indefinite-lived intangible assets	3.7	3.7
Trade/domain names
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived trade/domain names, gross amount	3.7	3.7
Finite-lived intangible assets, accumulated amortization	(1.6)	(0.9)
Finite-lived intangible assets, net amount	2.1	2.8
Software programs/platforms
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived software programs/platforms, gross amount	28.3	31.4
Finite-lived intangible assets, accumulated amortization	(19.4)	(13.3)
Finite-lived intangible assets, net amount	8.9	18.1
Customer base
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived customer base, gross amount	29.5	37.7
Finite-lived intangible assets, accumulated amortization	(18.0)	(21.7)
Finite-lived intangible assets, net amount	$ 11.5	$ 16.0