GOODWILL AND INTANGIBLE ASSETS - Goodwill by Reporting Units (Details) - USD ($) $ in Millions	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015
Goodwill:
Goodwill	$ 22,539	$ 22,496	$ 22,575	$ 22,349
Operating Segments | Global Consumer Banking | Reporting units | North America Global Consumer Banking
Goodwill:
Goodwill	$ 6,763
Goodwill	148.00%
Operating Segments | Global Consumer Banking | Reporting units | Asia Global Consumer Banking
Goodwill:
Goodwill	$ 5,092
Goodwill	157.00%
Operating Segments | Global Consumer Banking | Reporting units | Latin America Global Consumer Banking
Goodwill:
Goodwill	$ 1,142
Goodwill	180.00%
Operating Segments | Institutional Clients Group | Reporting units | ICG—Banking
Goodwill:
Goodwill	$ 2,791
Goodwill	194.00%
Operating Segments | Institutional Clients Group | Reporting units | ICG—Markets and Securities Services
Goodwill:
Goodwill	$ 6,671
Goodwill	115.00%
Operating Segments | Citi Holdings | Reporting units | Citi Holdings—Consumer Latin America
Goodwill:
Goodwill	$ 80
Goodwill	127.00%