LOANS - Consumer Loans (Details) $ in Millions	3 Months Ended
	Mar. 31, 2018 USD ($) category	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)
Loans
Number of loan categories | category	2
Loans, net of unearned income	$ 672,938		$ 667,034
Consumer
Loans
Total loans	324,357		332,919
Net unearned income	727		737
Loans, net of unearned income	325,084		333,656
Loans sold and/or reclassified to held-for-sale	800	$ 2,300
In U.S. offices | Consumer
Loans
Total loans	205,292		215,711
In U.S. offices | Consumer | Mortgage and real estate
Loans
Total loans	63,412		65,467
In U.S. offices | Consumer | Installment, revolving credit and other
Loans
Total loans	3,306		3,398
In U.S. offices | Consumer | Cards
Loans
Total loans	131,081		139,006
In U.S. offices | Consumer | Commercial and industrial
Loans
Total loans	7,493		7,840
In offices outside the U.S. | Consumer
Loans
Total loans	119,065		117,208
In offices outside the U.S. | Consumer | Mortgage and real estate
Loans
Total loans	44,833		44,081
In offices outside the U.S. | Consumer | Installment, revolving credit and other
Loans
Total loans	27,651		26,556
In offices outside the U.S. | Consumer | Cards
Loans
Total loans	25,993		26,257
In offices outside the U.S. | Consumer | Commercial and industrial
Loans
Total loans	20,526		20,238
In offices outside the U.S. | Consumer | Lease financing
Loans
Total loans	$ 62		$ 76