SECURITIZATIONS AND VARIABLE INTEREST ENTITIES - Funding Commitments (Details) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Funding Commitments for Significant Unconsolidated VIEs
Notional amount	$ 8,397	$ 8,313
Liquidity facilities Citigroup
Funding Commitments for Significant Unconsolidated VIEs
Notional amount	3,445	3,675
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	3,440	3,670
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 commitments Citigroup
Funding Commitments for Significant Unconsolidated VIEs
Notional amount	4,952	4,638
Loan commitments Citigroup | Asset-based financing
Funding Commitments for Significant Unconsolidated VIEs
Notional amount	2,143	2,266
Loan commitments Citigroup | Municipal securities tender option bond trusts (TOBs)
Funding Commitments for Significant Unconsolidated VIEs
Notional amount	0	0
Loan commitments Citigroup | Municipal investments
Funding Commitments for Significant Unconsolidated VIEs
Notional amount	2,660	2,225
Loan commitments Citigroup | Investment funds
Funding Commitments for Significant Unconsolidated VIEs
Notional amount	102	124
Loan commitments Citigroup | Other
Funding Commitments for Significant Unconsolidated VIEs
Notional amount	$ 47	$ 23