GOODWILL AND INTANGIBLE ASSETS - Goodwill by Reporting Units (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Goodwill:
Goodwill	$ 22,265	$ 21,659
Operating Segments | Global Consumer Banking | Reporting units | North America Global Consumer Banking
Goodwill:
Goodwill	$ 6,732
Fair value of goodwill as a percentage of allocated book value	148.00%
Operating Segments | Global Consumer Banking | Reporting units | Asia Global Consumer Banking
Goodwill:
Goodwill	$ 4,910
Fair value of goodwill as a percentage of allocated book value	157.00%
Operating Segments | Global Consumer Banking | Reporting units | Latin America Global Consumer Banking
Goodwill:
Goodwill	$ 1,151
Fair value of goodwill as a percentage of allocated book value	180.00%
Operating Segments | Institutional Clients Group | Reporting units | ICG—Banking
Goodwill:
Goodwill	$ 2,902
Fair value of goodwill as a percentage of allocated book value	194.00%
Operating Segments | Institutional Clients Group | Reporting units | ICG—Markets and Securities Services
Goodwill:
Goodwill	$ 6,554
Fair value of goodwill as a percentage of allocated book value	115.00%
Operating Segments | Citi Holdings | Reporting units | Citi Holdings—Consumer Latin America
Goodwill:
Goodwill	$ 16
Fair value of goodwill as a percentage of allocated book value	103.00%