Restricted Cash and Other Restricted Assets (Details) - USD ($) $ in Billions	Sep. 30, 2018	Dec. 31, 2017
Restricted Cash and Cash Equivalents Items [Line Items]
Total restricted cash	$ 42.2	$ 45.8
Cash and securities pledged with clearing organizations for the benefit of customers	18.8	18.0
Fair value of securities restricted in relation to customer activity	2.2	3.5
Deposits with banks
Restricted Cash and Cash Equivalents Items [Line Items]
Total restricted cash	40.7	44.8
Cash and due from banks
Restricted Cash and Cash Equivalents Items [Line Items]
Total restricted cash	1.5	1.0
Cash reserves – Federal Reserve Banks
Restricted Cash and Cash Equivalents Items [Line Items]
Total restricted cash	23.6	25.7
Segregated for the benefit of securities and futures brokerage customers
Restricted Cash and Cash Equivalents Items [Line Items]
Total restricted cash	15.3	16.8
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	$ 3.3	$ 3.3