GUARANTEES AND COMMITMENTS - Credit Commitments and Lines of Credit (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Guarantor Obligations
Credit commitments	$ 985,391	$ 968,296
Commercial and similar letters of credit
Guarantor Obligations
Credit commitments	5,188	5,736
One- to four-family residential mortgages
Guarantor Obligations
Credit commitments	3,270	2,838
Revolving open-end loans secured by one- to four-family residential properties
Guarantor Obligations
Credit commitments	13,038	13,405
Commercial real estate, construction and land development
Guarantor Obligations
Credit commitments	12,210	10,781
Credit card lines
Guarantor Obligations
Credit commitments	676,264	664,335
Commercial and other consumer loan commitments
Guarantor Obligations
Credit commitments	263,887	259,934
Other commitments and contingencies
Guarantor Obligations
Credit commitments	11,534	$ 11,267
U.S.
Guarantor Obligations
Credit commitments	772,612
U.S. | Commercial and similar letters of credit
Guarantor Obligations
Credit commitments	913
U.S. | One- to four-family residential mortgages
Guarantor Obligations
Credit commitments	1,589
U.S. | Revolving open-end loans secured by one- to four-family residential properties
Guarantor Obligations
Credit commitments	11,487
U.S. | Commercial real estate, construction and land development
Guarantor Obligations
Credit commitments	10,816
U.S. | Credit card lines
Guarantor Obligations
Credit commitments	577,326
U.S. | Commercial and other consumer loan commitments
Guarantor Obligations
Credit commitments	168,318
U.S. | Other commitments and contingencies
Guarantor Obligations
Credit commitments	2,163
Outside of U.S.
Guarantor Obligations
Credit commitments	212,779
Outside of U.S. | Commercial and similar letters of credit
Guarantor Obligations
Credit commitments	4,275
Outside of U.S. | One- to four-family residential mortgages
Guarantor Obligations
Credit commitments	1,681
Outside of U.S. | Revolving open-end loans secured by one- to four-family residential properties
Guarantor Obligations
Credit commitments	1,551
Outside of U.S. | Commercial real estate, construction and land development
Guarantor Obligations
Credit commitments	1,394
Outside of U.S. | Credit card lines
Guarantor Obligations
Credit commitments	98,938
Outside of U.S. | Commercial and other consumer loan commitments
Guarantor Obligations
Credit commitments	95,569
Outside of U.S. | Other commitments and contingencies
Guarantor Obligations
Credit commitments	$ 9,371