SECURITIZATIONS AND VARIABLE INTEREST ENTITIES - Funding Commitments (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Funding Commitments for Significant Unconsolidated VIEs
Notional amount	$ 16,109	$ 13,783
Liquidity facilities
Funding Commitments for Significant Unconsolidated VIEs
Notional amount	1,529	1,611
Liquidity facilities | Non-agency-sponsored mortgage securitizations
Funding Commitments for Significant Unconsolidated VIEs
Notional amount	0	0
Liquidity facilities | Asset-based financing
Funding Commitments for Significant Unconsolidated VIEs
Notional amount	0	0
Liquidity facilities | Municipal securities tender option bond trusts (TOBs)
Funding Commitments for Significant Unconsolidated VIEs
Notional amount	1,529	1,611
Liquidity facilities | Municipal investments
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	14,580	12,172
Loan / equity commitments | Non-agency-sponsored mortgage securitizations
Funding Commitments for Significant Unconsolidated VIEs
Notional amount	1	2
Loan / equity commitments | Asset-based financing
Funding Commitments for Significant Unconsolidated VIEs
Notional amount	11,008	9,114
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	3,558	3,041
Loan / equity commitments | Investment funds
Funding Commitments for Significant Unconsolidated VIEs
Notional amount	13	15
Loan / equity commitments | Other
Funding Commitments for Significant Unconsolidated VIEs
Notional amount	$ 0	$ 0