PLEDGED ASSETS, COLLATERAL, GUARANTEES AND COMMITMENTS - Restricted Cash (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash	$ 31,208	$ 30,815
Cash segregated under federal and other brokerage regulations or deposited with clearing organizations	8,300	7,400
Cash and due from banks
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash	4,000	3,151
Deposits with banks
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash	$ 27,208	$ 27,664