SECURITIZATIONS AND VARIABLE INTEREST ENTITIES - Funding, Liquidity Facilities and Subordinated Interests (Details) - USD ($) $ in Billions	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Citibank Credit Card Master Trust (Master Trust)
Funding, Liquidity Facilities and Subordinated Interests
Weighted average maturity of term notes	2 years 9 months 30 days	2 years 6 months 25 days
Term notes issued to third parties	$ 27.0	$ 21.7
Term notes retained by Citigroup affiliates	7.3	5.5
Total Master Trust liabilities	$ 34.3	$ 27.2
Citibank OMNI Master Trust (Omni Trust)
Funding, Liquidity Facilities and Subordinated Interests
Weighted average maturity of term notes	1 year 1 month	1 year 11 months
Term notes issued to third parties	$ 1.0	$ 1.0
Term notes retained by Citigroup affiliates	1.9	1.9
Total Master Trust liabilities	$ 2.9	$ 2.9