PLEDGED ASSETS, COLLATERAL, GUARANTEES AND COMMITMENTS - Credit Commitments and Lines of Credit (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Credit Commitments
Credit commitments	$ 1,018,894	$ 985,174
Unsettled reverse repurchase and securities borrowing agreements	36,100	35,000
Unsettled repurchase and securities lending agreements	30,700	19,100
Commercial and similar letters of credit
Credit Commitments
Credit commitments	5,461	5,000
One-to four-family residential mortgages
Credit Commitments
Credit commitments	2,671	2,674
Revolving open-end loans secured by one-to four-family residential properties
Credit Commitments
Credit commitments	11,374	12,323
Commercial real estate, construction and land development
Credit Commitments
Credit commitments	11,293	11,151
Credit card lines
Credit Commitments
Credit commitments	696,007	678,300
Commercial and other consumer loan commitments
Credit Commitments
Credit commitments	288,767	272,655
Other commitments and contingencies
Credit Commitments
Credit commitments	3,321	$ 3,071
U.S.
Credit Commitments
Credit commitments	815,729
U.S. | Commercial and similar letters of credit
Credit Commitments
Credit commitments	823
U.S. | One-to four-family residential mortgages
Credit Commitments
Credit commitments	1,056
U.S. | Revolving open-end loans secured by one-to four-family residential properties
Credit Commitments
Credit commitments	10,019
U.S. | Commercial real estate, construction and land development
Credit Commitments
Credit commitments	9,565
U.S. | Credit card lines
Credit Commitments
Credit commitments	605,857
U.S. | Commercial and other consumer loan commitments
Credit Commitments
Credit commitments	185,849
U.S. | Other commitments and contingencies
Credit Commitments
Credit commitments	2,560
Outside U.S.
Credit Commitments
Credit commitments	203,165
Outside U.S. | Commercial and similar letters of credit
Credit Commitments
Credit commitments	4,638
Outside U.S. | One-to four-family residential mortgages
Credit Commitments
Credit commitments	1,615
Outside U.S. | Revolving open-end loans secured by one-to four-family residential properties
Credit Commitments
Credit commitments	1,355
Outside U.S. | Commercial real estate, construction and land development
Credit Commitments
Credit commitments	1,728
Outside U.S. | Credit card lines
Credit Commitments
Credit commitments	90,150
Outside U.S. | Commercial and other consumer loan commitments
Credit Commitments
Credit commitments	102,918
Outside U.S. | Other commitments and contingencies
Credit Commitments
Credit commitments	$ 761