SECURITIZATIONS AND VARIABLE INTEREST ENTITIES - Funding Commitments (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Funding Commitments for Significant Unconsolidated VIEs
Notional amount	$ 13,783	$ 16,157
Liquidity facilities
Funding Commitments for Significant Unconsolidated VIEs
Notional amount	1,611	3,544
Loan / equity commitments
Funding Commitments for Significant Unconsolidated VIEs
Notional amount	12,172	12,613
Non-agency-sponsored mortgage securitizations | Liquidity facilities
Funding Commitments for Significant Unconsolidated VIEs
Notional amount	0	0
Non-agency-sponsored mortgage securitizations | Loan / equity commitments
Funding Commitments for Significant Unconsolidated VIEs
Notional amount	2	0
Asset-based financing | Liquidity facilities
Funding Commitments for Significant Unconsolidated VIEs
Notional amount	0	0
Asset-based financing | Loan / equity commitments
Funding Commitments for Significant Unconsolidated VIEs
Notional amount	9,114	9,524
Municipal securities tender option bond trusts (TOBs) | Liquidity facilities
Funding Commitments for Significant Unconsolidated VIEs
Notional amount	1,611	3,544
Municipal securities tender option bond trusts (TOBs) | Loan / equity commitments
Funding Commitments for Significant Unconsolidated VIEs
Notional amount	0	0
Municipal investments | Liquidity facilities
Funding Commitments for Significant Unconsolidated VIEs
Notional amount	0	0
Municipal investments | Loan / equity commitments
Funding Commitments for Significant Unconsolidated VIEs
Notional amount	3,041	3,034
Investment funds | Liquidity facilities
Funding Commitments for Significant Unconsolidated VIEs
Notional amount	0	0
Investment funds | Loan / equity commitments
Funding Commitments for Significant Unconsolidated VIEs
Notional amount	15	16
Other | Liquidity facilities
Funding Commitments for Significant Unconsolidated VIEs
Notional amount	0	0
Other | Loan / equity commitments
Funding Commitments for Significant Unconsolidated VIEs
Notional amount	$ 0	$ 39