LOANS - Corporate Loans (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Loans
Loans, net of unearned income	$ 638,435		$ 638,435		$ 617,617
Corporate
Loans
Total loans	310,411		310,411		292,497
Net unearned income	(678)		(678)		(665)
Loans, net of unearned income	309,733		309,733		291,832
Loans sold and/or reclassified to held-for-sale	1,300	$ 500	2,600	$ 1,600
Corporate | Commercial and industrial
Loans
Loans, net of unearned income	131,683		131,683		119,627
Corporate | Financial institutions
Loans
Loans, net of unearned income	62,472		62,472		64,317
Corporate | Mortgage and real estate
Loans
Loans, net of unearned income	46,571		46,571		42,471
Corporate | Lease financing
Loans
Loans, net of unearned income	1,774		1,774		2,082
Corporate | In U.S. offices
Loans
Total loans	161,138		161,138		150,262
Corporate | In U.S. offices | Commercial and industrial
Loans
Total loans	50,156		50,156		41,147
Corporate | In U.S. offices | Financial institutions
Loans
Total loans	35,801		35,801		36,396
Corporate | In U.S. offices | Mortgage and real estate
Loans
Total loans	41,078		41,078		37,565
Corporate | In U.S. offices | Installment, revolving credit, and other
Loans
Total loans	32,571		32,571		33,374
Corporate | In U.S. offices | Lease financing
Loans
Total loans	1,532		1,532		1,780
Corporate | In offices outside the U.S.
Loans
Total loans	149,273		149,273		142,235
Corporate | In offices outside the U.S. | Commercial and industrial
Loans
Total loans	84,162		84,162		82,358
Corporate | In offices outside the U.S. | Financial institutions
Loans
Total loans	27,305		27,305		28,704
Corporate | In offices outside the U.S. | Mortgage and real estate
Loans
Total loans	5,595		5,595		5,106
Corporate | In offices outside the U.S. | Installment, revolving credit, and other
Loans
Total loans	25,462		25,462		20,853
Corporate | In offices outside the U.S. | Lease financing
Loans
Total loans	243		243		303
Corporate | In offices outside the U.S. | Government and official institutions
Loans
Total loans	$ 6,506		$ 6,506		$ 4,911