LOANS - Consumer Loans (Details) $ in Millions	3 Months Ended
	Mar. 31, 2017 USD ($) category	Mar. 31, 2016 USD ($)	Dec. 31, 2016 USD ($)
Loans
Number of loan categories | category	2
Loans, net of unearned income	$ 628,595		$ 624,369
Consumer
Loans
Total loans	319,799		324,287
Net unearned income	757		776
Loans, net of unearned income	320,556		325,063
Loans sold and/or reclassified to held-for-sale	2,300	$ 2,700
In U.S. offices | Consumer
Loans
Total loans	207,655		216,165
In U.S. offices | Consumer | Mortgage and real estate
Loans
Total loans	71,170		72,957
In U.S. offices | Consumer | Installment, revolving credit, and other
Loans
Total loans	3,252		3,395
In U.S. offices | Consumer | Cards
Loans
Total loans	125,799		132,654
In U.S. offices | Consumer | Commercial and industrial
Loans
Total loans	7,434		7,159
In offices outside the U.S. | Consumer
Loans
Total loans	112,144		108,122
In offices outside the U.S. | Consumer | Mortgage and real estate
Loans
Total loans	43,822		42,803
In offices outside the U.S. | Consumer | Installment, revolving credit, and other
Loans
Total loans	26,014		24,887
In offices outside the U.S. | Consumer | Cards
Loans
Total loans	24,497		23,783
In offices outside the U.S. | Consumer | Commercial and industrial
Loans
Total loans	17,728		16,568
In offices outside the U.S. | Consumer | Lease financing
Loans
Total loans	$ 83		$ 81