FAIR VALUE ELECTIONS - Changes in Fair Value Gains (Losses) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Federal funds sold and securities borrowed or purchased under agreements to resell selected portfolios of securities purchased under agreements to resell and securities borrowed
Fair Value, Balance Sheet Grouping, Financial Statement Captions.
Fair value elections, changes in fair value gains (losses)	$ 28	$ 2
Trading account assets
Fair Value, Balance Sheet Grouping, Financial Statement Captions.
Fair value elections, changes in fair value gains (losses)	258	91
Investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions.
Fair value elections, changes in fair value gains (losses)	1	45
Corporate
Fair Value, Balance Sheet Grouping, Financial Statement Captions.
Fair value elections, changes in fair value gains (losses)	24	(49)
Consumer loans
Fair Value, Balance Sheet Grouping, Financial Statement Captions.
Fair value elections, changes in fair value gains (losses)	(1)	2
Loans
Fair Value, Balance Sheet Grouping, Financial Statement Captions.
Fair value elections, changes in fair value gains (losses)	23	(47)
Mortgage servicing rights
Fair Value, Balance Sheet Grouping, Financial Statement Captions.
Fair value elections, changes in fair value gains (losses)	(225)	(71)
Certain mortgage loans (HFS)
Fair Value, Balance Sheet Grouping, Financial Statement Captions.
Fair value elections, changes in fair value gains (losses)	80	102
Other assets
Fair Value, Balance Sheet Grouping, Financial Statement Captions.
Fair value elections, changes in fair value gains (losses)	370	0
Total other assets
Fair Value, Balance Sheet Grouping, Financial Statement Captions.
Fair value elections, changes in fair value gains (losses)	225	31
Total assets
Fair Value, Balance Sheet Grouping, Financial Statement Captions.
Fair value elections, changes in fair value gains (losses)	535	122
Interest-bearing deposits
Fair Value, Balance Sheet Grouping, Financial Statement Captions.
Fair value elections, changes in fair value gains (losses)	(50)	10
Federal funds purchased and securities loaned or sold under agreements to repurchase selected portfolios of securities sold under agreements to repurchase and securities loaned
Fair Value, Balance Sheet Grouping, Financial Statement Captions.
Fair value elections, changes in fair value gains (losses)	(6)	2
Trading account liabilities
Fair Value, Balance Sheet Grouping, Financial Statement Captions.
Fair value elections, changes in fair value gains (losses)	94	29
Short-term borrowings
Fair Value, Balance Sheet Grouping, Financial Statement Captions.
Fair value elections, changes in fair value gains (losses)	80	(1)
Long-term debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions.
Fair value elections, changes in fair value gains (losses)	(423)	189
Total liabilities
Fair Value, Balance Sheet Grouping, Financial Statement Captions.
Fair value elections, changes in fair value gains (losses)	$ (305)	$ 229