Basis of Presentation and Consolidation and Accounting Standards Adopted (Details) $ in Millions		3 Months Ended		9 Months Ended
	Oct. 01, 2020 USD ($) client	Jun. 30, 2022 USD ($) client country	Jun. 30, 2021 USD ($)	Jun. 30, 2022 USD ($) client country	Jun. 30, 2021 USD ($)	Sep. 30, 2021 USD ($)
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of countries in which entity operates | country		180		180
Number of commercial and institutional clients | client		52,000		52,000
Number retail clients | client		370,000		370,000
Cumulative-effect adjustment, net of tax		$ 837.3		$ 837.3		$ 682.5
Income tax expense		$ 21.8	$ 11.8	$ 56.0	$ 40.2
Cumulative Effect, Period of Adoption, Adjustment
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Cumulative-effect adjustment, net of tax	$ (6.2)
Income tax expense	$ 2.0
Number of client deficit accounts impacted | client	300
Retail Segment
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of countries in which entity operates | country		180		180