SECURITIZATIONS AND VARIABLE INTEREST ENTITIES - Funding Commitments (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Funding Commitments for Significant Unconsolidated VIEs
Notional amount	$ 10,968	$ 10,422
Liquidity facilities
Funding Commitments for Significant Unconsolidated VIEs
Notional amount	3,063	2,847
Liquidity facilities | Asset-based financing
Funding Commitments for Significant Unconsolidated VIEs
Notional amount	0	5
Liquidity facilities | Municipal securities tender option bond trusts (TOBs)
Funding Commitments for Significant Unconsolidated VIEs
Notional amount	3,063	2,842
Liquidity facilities | Municipal investments
Funding Commitments for Significant Unconsolidated VIEs
Notional amount	0	0
Liquidity facilities | Client intermediation
Funding Commitments for Significant Unconsolidated VIEs
Notional amount	0	0
Liquidity facilities | Investment funds
Funding Commitments for Significant Unconsolidated VIEs
Notional amount	0	0
Liquidity facilities | Other
Funding Commitments for Significant Unconsolidated VIEs
Notional amount	0	0
Loan / equity commitments
Funding Commitments for Significant Unconsolidated VIEs
Notional amount	7,905	7,575
Loan / equity commitments | Asset-based financing
Funding Commitments for Significant Unconsolidated VIEs
Notional amount	5,016	4,910
Loan / equity commitments | Municipal securities tender option bond trusts (TOBs)
Funding Commitments for Significant Unconsolidated VIEs
Notional amount	0	0
Loan / equity commitments | Municipal investments
Funding Commitments for Significant Unconsolidated VIEs
Notional amount	2,345	2,580
Loan / equity commitments | Client intermediation
Funding Commitments for Significant Unconsolidated VIEs
Notional amount	491	0
Loan / equity commitments | Investment funds
Funding Commitments for Significant Unconsolidated VIEs
Notional amount	15	27
Loan / equity commitments | Other
Funding Commitments for Significant Unconsolidated VIEs
Notional amount	$ 38	$ 58