SECURITIZATIONS AND VARIABLE INTEREST ENTITIES - Funding, Liquidity Facilities and Subordinated Interests (Details) - USD ($) $ in Billions	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Citibank Credit Card Master Trust (Master Trust)
Funding, Liquidity Facilities and Subordinated Interests
Weighted average maturity of term notes	3 years 1 month 6 days	3 years
Term notes issued to third parties	$ 23.3	$ 25.8
Term notes retained by Citigroup affiliates	5.7	5.7
Total Master Trust liabilities	$ 29.0	$ 31.5
Citibank OMNI Master Trust (Omni Trust)
Funding, Liquidity Facilities and Subordinated Interests
Weighted average maturity of term notes	1 year 2 months 12 days	1 year 4 months 24 days
Term notes issued to third parties	$ 1.5	$ 1.5
Term notes retained by Citigroup affiliates	1.9	1.9
Total Master Trust liabilities	$ 3.4	$ 3.4