Restricted Cash and Other Restricted Assets (Details) - USD ($) $ in Billions	Sep. 30, 2021	Dec. 31, 2020
Restricted Cash and Cash Equivalents Items [Line Items]
Total restricted cash	$ 21.3	$ 24.4
Cash and securities pledged with clearing organizations for the benefit of customers	45.7	37.2
Fair value of securities restricted in relation to customer activity	24.2	1.3
Deposits with banks
Restricted Cash and Cash Equivalents Items [Line Items]
Total restricted cash	20.0	22.7
Cash and due from banks
Restricted Cash and Cash Equivalents Items [Line Items]
Total restricted cash	1.3	1.7
Segregated for the benefit of securities and cleared derivative customers
Restricted Cash and Cash Equivalents Items [Line Items]
Total restricted cash	16.2	19.3
Cash reserves at non-U.S. central banks and held for other general purposes
Restricted Cash and Cash Equivalents Items [Line Items]
Total restricted cash	$ 5.1	$ 5.1