LOANS - Consumer Loans (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016 USD ($) category	Sep. 30, 2015 USD ($)	Sep. 30, 2016 USD ($) category	Sep. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)
Loans
Number of loan categories | category	2		2
Loans, net of unearned income	$ 638,435		$ 638,435		$ 617,617
Consumer
Loans
Total loans	327,890		327,890		324,955
Net unearned income	812		812		830
Loans, net of unearned income	328,702		328,702		325,785
Loans sold and/or reclassified to held-for-sale	1,300	$ 1,500	6,000	$ 16,300
In U.S. offices | Consumer
Loans
Total loans	210,148		210,148		202,968
In U.S. offices | Consumer | Mortgage and real estate
Loans
Total loans	75,057		75,057		80,281
In U.S. offices | Consumer | Installment, revolving credit, and other
Loans
Total loans	3,465		3,465		3,480
In U.S. offices | Consumer | Cards
Loans
Total loans	124,637		124,637		112,800
In U.S. offices | Consumer | Commercial and industrial
Loans
Total loans	6,989		6,989		6,407
In offices outside the U.S. | Consumer
Loans
Total loans	117,742		117,742		121,987
In offices outside the U.S. | Consumer | Mortgage and real estate
Loans
Total loans	45,751		45,751		47,062
In offices outside the U.S. | Consumer | Installment, revolving credit, and other
Loans
Total loans	28,217		28,217		29,480
In offices outside the U.S. | Consumer | Cards
Loans
Total loans	25,833		25,833		27,342
In offices outside the U.S. | Consumer | Commercial and industrial
Loans
Total loans	17,828		17,828		17,741
In offices outside the U.S. | Consumer | Lease financing
Loans
Total loans	$ 113		$ 113		$ 362