Pledged Assets, Accepted Collateral and Restricted Assets (Accepted Collateral) (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Customer Securities for which Entity has Right to Sell or Repledge (Including Securities Sold or Repledged) [Line Items]
Total Collateral Accepted	$ 65,334.7	$ 62,780.0
Fair value of securities received as collateral that have been resold or repledged	64,800.0	62,000.0
Reverse repurchase agreements
Customer Securities for which Entity has Right to Sell or Repledge (Including Securities Sold or Repledged) [Line Items]
Collateral that may be repledged or sold	65,311.1	62,767.8
Derivative contracts
Customer Securities for which Entity has Right to Sell or Repledge (Including Securities Sold or Repledged) [Line Items]
Collateral that may be repledged or sold	$ 23.6	$ 12.2