GUARANTEES, LEASES AND COMMITMENTS - Credit Commitments and Lines of Credit (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Guarantor Obligations
Credit commitments	$ 1,036,694	$ 1,066,364
Unsettled reverse repurchase and securities borrowing agreements	67,800	34,000
Unsettled repurchase and securities lending agreements	59,600	38,700
Commercial and similar letters of credit
Guarantor Obligations
Credit commitments	4,616	4,533
One- to four-family residential mortgages
Guarantor Obligations
Credit commitments	4,749	3,721
Revolving open-end loans secured by one- to four-family residential properties
Guarantor Obligations
Credit commitments	10,419	10,799
Commercial real estate, construction and land development
Guarantor Obligations
Credit commitments	11,390	12,981
Credit card lines
Guarantor Obligations
Credit commitments	716,550	708,023
Commercial and other consumer loan commitments
Guarantor Obligations
Credit commitments	285,685	324,359
Other commitments and contingencies
Guarantor Obligations
Credit commitments	3,285	$ 1,948
U.S.
Guarantor Obligations
Credit commitments	828,586
U.S. | Commercial and similar letters of credit
Guarantor Obligations
Credit commitments	717
U.S. | One- to four-family residential mortgages
Guarantor Obligations
Credit commitments	2,862
U.S. | Revolving open-end loans secured by one- to four-family residential properties
Guarantor Obligations
Credit commitments	9,220
U.S. | Commercial real estate, construction and land development
Guarantor Obligations
Credit commitments	8,801
U.S. | Credit card lines
Guarantor Obligations
Credit commitments	621,188
U.S. | Commercial and other consumer loan commitments
Guarantor Obligations
Credit commitments	183,973
U.S. | Other commitments and contingencies
Guarantor Obligations
Credit commitments	1,825
Outside of U.S.
Guarantor Obligations
Credit commitments	208,108
Outside of U.S. | Commercial and similar letters of credit
Guarantor Obligations
Credit commitments	3,899
Outside of U.S. | One- to four-family residential mortgages
Guarantor Obligations
Credit commitments	1,887
Outside of U.S. | Revolving open-end loans secured by one- to four-family residential properties
Guarantor Obligations
Credit commitments	1,199
Outside of U.S. | Commercial real estate, construction and land development
Guarantor Obligations
Credit commitments	2,589
Outside of U.S. | Credit card lines
Guarantor Obligations
Credit commitments	95,362
Outside of U.S. | Commercial and other consumer loan commitments
Guarantor Obligations
Credit commitments	101,712
Outside of U.S. | Other commitments and contingencies
Guarantor Obligations
Credit commitments	$ 1,460