LOANS - Consumer Loans (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019 USD ($) category	Mar. 31, 2018 USD ($)	Dec. 31, 2018 USD ($)
Loans
Number of loan categories | category	2
Loans, net of unearned income	$ 682,346		$ 684,196
Consumer
Loans
Total loans	319,186		329,779
Net unearned income	701		708
Loans, net of unearned income	319,887		330,487
Loans sold and/or reclassified to held-for-sale	1,900	$ 800
In U.S. offices | Consumer
Loans
Total loans	204,783		215,569
In U.S. offices | Consumer | Mortgage and real estate
Loans
Total loans	57,461		60,127
In U.S. offices | Consumer | Installment, revolving credit and other
Loans
Total loans	3,257		3,398
In U.S. offices | Consumer | Cards
Loans
Total loans	135,206		143,788
In U.S. offices | Consumer | Commercial and industrial
Loans
Total loans	8,859		8,256
In offices outside the U.S. | Consumer
Loans
Total loans	114,403		114,210
In offices outside the U.S. | Consumer | Mortgage and real estate
Loans
Total loans	43,184		43,379
In offices outside the U.S. | Consumer | Installment, revolving credit and other
Loans
Total loans	27,525		27,609
In offices outside the U.S. | Consumer | Cards
Loans
Total loans	24,763		25,400
In offices outside the U.S. | Consumer | Commercial and industrial
Loans
Total loans	18,884		17,773
In offices outside the U.S. | Consumer | Lease financing
Loans
Total loans	$ 47		$ 49