Pledged Assets, Accepted Collateral and Restricted Assets (Accepted Collateral) (Details) - USD ($) $ in Millions	Jun. 30, 2026	Dec. 31, 2025
Financial Instruments Owned and Pledged as Collateral [Line Items]
Total Collateral Accepted	$ 92,564.5	$ 90,478.1
Reverse repurchase agreements
Financial Instruments Owned and Pledged as Collateral [Line Items]
Collateral that may be repledged or sold	92,474.8	90,475.4
Fair value of securities received as collateral that have been resold or repledged	92,000.0	89,700.0
Derivative contracts
Financial Instruments Owned and Pledged as Collateral [Line Items]
Collateral that may be repledged or sold	$ 89.7	$ 2.7