GOODWILL AND INTANGIBLE ASSETS - Goodwill by Reporting Units (Details) $ in Millions			3 Months Ended	6 Months Ended
	Jun. 30, 2015 USD ($)	Jan. 01, 2015 reporting_unit	Mar. 31, 2015 USD ($)	Jun. 30, 2015 USD ($)	Dec. 31, 2014 USD ($)
Goodwill:
Number of new reporting units | reporting_unit		5
Impairments			$ 16
Goodwill	$ 23,012		23,150	$ 23,012	$ 23,592
Operating Segments | Global Consumer Banking | Reporting units | North America Global Consumer Banking
Goodwill:
Goodwill	6,729			6,729
Operating Segments | Global Consumer Banking | Reporting units | EMEA Global Consumer Banking
Goodwill:
Goodwill	310			310
Operating Segments | Global Consumer Banking | Reporting units | Asia Global Consumer Banking
Goodwill:
Goodwill	4,589			4,589
Operating Segments | Global Consumer Banking | Reporting units | Latin America Global Consumer Banking
Goodwill:
Goodwill	1,442			1,442
Operating Segments | Institutional Clients Group | Reporting units | Banking
Goodwill:
Goodwill	3,293			3,293
Operating Segments | Institutional Clients Group | Reporting units | Markets and Securities Services
Goodwill:
Goodwill	6,566			6,566
Operating Segments | Citi Holdings | Reporting units | Citi Holdings—Consumer EMEA
Goodwill:
Goodwill, reclassified to other assets held-for-sale				13
Fair Value as a % of allocated book value		107.00%
Goodwill	13			13
Operating Segments | Citi Holdings | Reporting units | Citi Holdings — Consumer Japan
Goodwill:
Goodwill	$ 0			0
Operating Segments | Citi Holdings | Reporting units | Citi Holdings—Consumer Latin America
Goodwill:
Goodwill, reclassified to other assets held-for-sale				70
Fair Value as a % of allocated book value	101.00%
Goodwill	$ 70			$ 70
Operating Segments | Citi Holdings | Reporting units | Consumer Finance South Korea
Goodwill:
Impairments			$ 16