GOODWILL AND INTANGIBLE ASSETS - Goodwill by Reporting Units (Details) - USD ($) $ in Millions	3 Months Ended
	Sep. 30, 2015	Mar. 31, 2015	Jun. 30, 2015	Dec. 31, 2014
Goodwill:
Impairments	$ 15	$ 16
Goodwill	22,444	23,150	$ 23,012	$ 23,592
Operating Segments | Global Consumer Banking | Reporting units | North America Global Consumer Banking
Goodwill:
Goodwill	6,714
Operating Segments | Global Consumer Banking | Reporting units | EMEA Global Consumer Banking
Goodwill:
Goodwill	299
Operating Segments | Global Consumer Banking | Reporting units | Asia Global Consumer Banking
Goodwill:
Goodwill	4,504
Operating Segments | Global Consumer Banking | Reporting units | Latin America Global Consumer Banking
Goodwill:
Goodwill	1,343
Operating Segments | Institutional Clients Group | Reporting units | Banking
Goodwill:
Goodwill	3,104
Operating Segments | Institutional Clients Group | Reporting units | Markets and Securities Services
Goodwill:
Goodwill	6,480
Operating Segments | Citi Holdings | Reporting units | Citi Holdings—Consumer Finance South Korea
Goodwill:
Impairments		$ 16
Operating Segments | Citi Holdings | Reporting units | Citi Holdings—Consumer Latin America
Goodwill:
Impairments	15
Goodwill, reclassified to other assets held-for-sale	55
Operating Segments | Citi Holdings | Reporting units | Citi Holdings—Consumer EMEA
Goodwill:
Goodwill, reclassified to other assets held-for-sale	$ 13