GUARANTEES AND COMMITMENTS - Credit Commitments and Lines of Credit (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Guarantor Obligations
Credit commitments	$ 990,182	$ 968,296
Commercial and similar letters of credit
Guarantor Obligations
Credit commitments	5,585	5,736
One- to four-family residential mortgages
Guarantor Obligations
Credit commitments	2,981	2,838
Revolving open-end loans secured by one- to four-family residential properties
Guarantor Obligations
Credit commitments	13,442	13,405
Commercial real estate, construction and land development
Guarantor Obligations
Credit commitments	10,880	10,781
Credit card lines
Guarantor Obligations
Credit commitments	673,688	664,335
Commercial and other consumer loan commitments
Guarantor Obligations
Credit commitments	270,593	259,934
Other commitments and contingencies
Guarantor Obligations
Credit commitments	13,013	$ 11,267
U.S.
Guarantor Obligations
Credit commitments	778,094
U.S. | Commercial and similar letters of credit
Guarantor Obligations
Credit commitments	795
U.S. | One- to four-family residential mortgages
Guarantor Obligations
Credit commitments	1,283
U.S. | Revolving open-end loans secured by one- to four-family residential properties
Guarantor Obligations
Credit commitments	11,900
U.S. | Commercial real estate, construction and land development
Guarantor Obligations
Credit commitments	9,562
U.S. | Credit card lines
Guarantor Obligations
Credit commitments	576,402
U.S. | Commercial and other consumer loan commitments
Guarantor Obligations
Credit commitments	174,429
U.S. | Other commitments and contingencies
Guarantor Obligations
Credit commitments	3,723
Outside of U.S.
Guarantor Obligations
Credit commitments	212,088
Outside of U.S. | Commercial and similar letters of credit
Guarantor Obligations
Credit commitments	4,790
Outside of U.S. | One- to four-family residential mortgages
Guarantor Obligations
Credit commitments	1,698
Outside of U.S. | Revolving open-end loans secured by one- to four-family residential properties
Guarantor Obligations
Credit commitments	1,542
Outside of U.S. | Commercial real estate, construction and land development
Guarantor Obligations
Credit commitments	1,318
Outside of U.S. | Credit card lines
Guarantor Obligations
Credit commitments	97,286
Outside of U.S. | Commercial and other consumer loan commitments
Guarantor Obligations
Credit commitments	96,164
Outside of U.S. | Other commitments and contingencies
Guarantor Obligations
Credit commitments	$ 9,290