Commitments and Contingencies (Other Commitments) (Details) - USD ($) $ in Millions	Mar. 31, 2026	Dec. 31, 2025
Broker-Dealer [Abstract]
Collateral securities	$ 753.4
Collateral security (Fair value)	1,100.0
Amount pledged with client-owned securities	399.7
Remaining collateral securities that can be re-pledged, loaned, or sold	655.1
Financial Instruments Owned and Pledged as Collateral [Line Items]
Remaining collateral securities that can be re-pledged, loaned, or sold	655.1
Options Clearing Corporation [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Marketable Securities	14.8	$ 15.0
National Securities Clearing Corporation [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Marketable Securities	$ 24.7	$ 25.0

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The carrying value as of the balance sheet date of securities received as collateral from a counterparty that were re-pledged, sold, delivered or otherwise reused by the entity.

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Fair value as of the balance sheet date of customer securities accepted as collateral by the entity that it is permitted by contract or custom to sell or re-pledge to counterparties as collateral.

+ References

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Fair value as of the balance sheet date of customer securities accepted as collateral by the entity that it has sold or re-pledged to counterparties as collateral.

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Fair value of collateral permitted, by contact or custom, to be sold or re-pledged.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount of investment in marketable security.

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