SECURITIZATIONS AND VARIABLE INTEREST ENTITIES - Funding Commitments (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Funding Commitments for Significant Unconsolidated VIEs
Total funding commitments	$ 16,351	$ 16,883
Liquidity facilities
Funding Commitments for Significant Unconsolidated VIEs
Total funding commitments	0	417
Loan/equity commitments
Funding Commitments for Significant Unconsolidated VIEs
Total funding commitments	16,351	16,466
Non-agency-sponsored mortgage securitizations | Liquidity facilities
Funding Commitments for Significant Unconsolidated VIEs
Total funding commitments	0	0
Non-agency-sponsored mortgage securitizations | Loan/equity commitments
Funding Commitments for Significant Unconsolidated VIEs
Total funding commitments	566	129
Citi-administered asset-backed commercial paper conduits | Liquidity facilities
Funding Commitments for Significant Unconsolidated VIEs
Total funding commitments	0	0
Citi-administered asset-backed commercial paper conduits | Loan/equity commitments
Funding Commitments for Significant Unconsolidated VIEs
Total funding commitments	0	0
Asset-based financing | Liquidity facilities
Funding Commitments for Significant Unconsolidated VIEs
Total funding commitments	0	0
Asset-based financing | Loan/equity commitments
Funding Commitments for Significant Unconsolidated VIEs
Total funding commitments	13,185	13,655
Municipal securities tender option bond trusts (TOBs) | Liquidity facilities
Funding Commitments for Significant Unconsolidated VIEs
Total funding commitments	0	417
Municipal securities tender option bond trusts (TOBs) | Loan/equity commitments
Funding Commitments for Significant Unconsolidated VIEs
Total funding commitments	0	0
Municipal investments | Liquidity facilities
Funding Commitments for Significant Unconsolidated VIEs
Total funding commitments	0	0
Municipal investments | Loan/equity commitments
Funding Commitments for Significant Unconsolidated VIEs
Total funding commitments	2,502	2,587
Investment funds | Liquidity facilities
Funding Commitments for Significant Unconsolidated VIEs
Total funding commitments	0	0
Investment funds | Loan/equity commitments
Funding Commitments for Significant Unconsolidated VIEs
Total funding commitments	$ 98	$ 95