LOANS - Consumer Loans (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017 USD ($) category	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) category	Sep. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)
Loans
Number of loan categories | category	2		2
Loans, net of unearned income	$ 653,183		$ 653,183		$ 624,369
Consumer
Loans
Total loans	324,828		324,828		324,287
Net unearned income	748		748		776
Loans, net of unearned income	325,576		325,576		325,063
Loans sold and/or reclassified to held-for-sale	400	$ 1,300	3,200	$ 6,000
In U.S. offices | Consumer
Loans
Total loans	209,417		209,417		216,165
In U.S. offices | Consumer | Mortgage and real estate
Loans
Total loans	67,131		67,131		72,957
In U.S. offices | Consumer | Installment, revolving credit and other
Loans
Total loans	3,191		3,191		3,395
In U.S. offices | Consumer | Cards
Loans
Total loans	131,476		131,476		132,654
In U.S. offices | Consumer | Commercial and industrial
Loans
Total loans	7,619		7,619		7,159
In offices outside the U.S. | Consumer
Loans
Total loans	115,411		115,411		108,122
In offices outside the U.S. | Consumer | Mortgage and real estate
Loans
Total loans	43,723		43,723		42,803
In offices outside the U.S. | Consumer | Installment, revolving credit and other
Loans
Total loans	26,153		26,153		24,887
In offices outside the U.S. | Consumer | Cards
Loans
Total loans	25,443		25,443		23,783
In offices outside the U.S. | Consumer | Commercial and industrial
Loans
Total loans	20,015		20,015		16,568
In offices outside the U.S. | Consumer | Lease financing
Loans
Total loans	$ 77		$ 77		$ 81