LOANS - Consumer Loans (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($) category	Dec. 31, 2017 USD ($)
Loans
Number of loan categories | category	2
Loans, net of unearned income	$ 684,196	$ 667,034
Consumer
Loans
Total loans	329,779	332,919
Net unearned income	708	737
Loans, net of unearned income	330,487	333,656
Loans sold and/or reclassified to held-for-sale	3,200	4,900
In U.S. offices | Consumer
Loans
Total loans	215,569	215,711
In U.S. offices | Consumer | Mortgage and real estate
Loans
Total loans	60,127	65,467
In U.S. offices | Consumer | Installment, revolving credit and other
Loans
Total loans	3,398	3,398
In U.S. offices | Consumer | Cards
Loans
Total loans	143,788	139,006
In U.S. offices | Consumer | Commercial and industrial
Loans
Total loans	8,256	7,840
In offices outside the U.S. | Consumer
Loans
Total loans	114,210	117,208
In offices outside the U.S. | Consumer | Mortgage and real estate
Loans
Total loans	43,379	44,081
In offices outside the U.S. | Consumer | Installment, revolving credit and other
Loans
Total loans	27,609	26,556
In offices outside the U.S. | Consumer | Cards
Loans
Total loans	25,400	26,257
In offices outside the U.S. | Consumer | Commercial and industrial
Loans
Total loans	17,773	20,238
In offices outside the U.S. | Consumer | Lease financing
Loans
Total loans	$ 49	$ 76