SECURITIZATIONS AND VARIABLE INTEREST ENTITIES - Funding Commitments (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Funding Commitments for Significant Unconsolidated VIEs
Notional amount	$ 9,508	$ 9,153
Liquidity facilities Citigroup
Funding Commitments for Significant Unconsolidated VIEs
Notional amount	2,967	3,105
Liquidity facilities Citigroup | Asset-based financing
Funding Commitments for Significant Unconsolidated VIEs
Notional amount	5	5
Liquidity facilities Citigroup | Municipal securities tender option bond trusts (TOBs)
Funding Commitments for Significant Unconsolidated VIEs
Notional amount	2,962	3,100
Liquidity facilities Citigroup | Municipal investments
Funding Commitments for Significant Unconsolidated VIEs
Notional amount	0	0
Liquidity facilities Citigroup | Investment funds
Funding Commitments for Significant Unconsolidated VIEs
Notional amount	0	0
Liquidity facilities Citigroup | Other
Funding Commitments for Significant Unconsolidated VIEs
Notional amount	0	0
Loan / equity commitments Citigroup
Funding Commitments for Significant Unconsolidated VIEs
Notional amount	6,541	6,048
Loan / equity commitments Citigroup | Asset-based financing
Funding Commitments for Significant Unconsolidated VIEs
Notional amount	3,993	3,611
Loan / equity commitments Citigroup | Municipal securities tender option bond trusts (TOBs)
Funding Commitments for Significant Unconsolidated VIEs
Notional amount	0	0
Loan / equity commitments Citigroup | Municipal investments
Funding Commitments for Significant Unconsolidated VIEs
Notional amount	2,399	2,335
Loan / equity commitments Citigroup | Investment funds
Funding Commitments for Significant Unconsolidated VIEs
Notional amount	78	102
Loan / equity commitments Citigroup | Other
Funding Commitments for Significant Unconsolidated VIEs
Notional amount	$ 71	$ 0