PLEDGED ASSETS, COLLATERAL, GUARANTEES AND COMMITMENTS - Credit Commitments and Lines of Credit (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Credit Commitments
Credit commitments	$ 985,174	$ 960,231
Unsettled reverse repurchase and securities borrowing agreements	35,000	43,100
Unsettled repurchase and securities lending agreements	19,100	14,900
Commercial and similar letters of credit
Credit Commitments
Credit commitments	5,000	5,736
One-to four-family residential mortgages
Credit Commitments
Credit commitments	2,674	2,838
Revolving open-end loans secured by one-to four-family residential properties
Credit Commitments
Credit commitments	12,323	13,405
Commercial real estate, construction and land development
Credit Commitments
Credit commitments	11,151	10,781
Credit card lines
Credit Commitments
Credit commitments	678,300	664,335
Commercial and other consumer loan commitments
Credit Commitments
Credit commitments	272,655	259,934
Other commitments and contingencies
Credit Commitments
Credit commitments	3,071	$ 3,202
U.S.
Credit Commitments
Credit commitments	774,510
U.S. | Commercial and similar letters of credit
Credit Commitments
Credit commitments	904
U.S. | One-to four-family residential mortgages
Credit Commitments
Credit commitments	988
U.S. | Revolving open-end loans secured by one-to four-family residential properties
Credit Commitments
Credit commitments	10,825
U.S. | Commercial real estate, construction and land development
Credit Commitments
Credit commitments	9,594
U.S. | Credit card lines
Credit Commitments
Credit commitments	578,634
U.S. | Commercial and other consumer loan commitments
Credit Commitments
Credit commitments	171,383
U.S. | Other commitments and contingencies
Credit Commitments
Credit commitments	2,182
Outside U.S.
Credit Commitments
Credit commitments	210,664
Outside U.S. | Commercial and similar letters of credit
Credit Commitments
Credit commitments	4,096
Outside U.S. | One-to four-family residential mortgages
Credit Commitments
Credit commitments	1,686
Outside U.S. | Revolving open-end loans secured by one-to four-family residential properties
Credit Commitments
Credit commitments	1,498
Outside U.S. | Commercial real estate, construction and land development
Credit Commitments
Credit commitments	1,557
Outside U.S. | Credit card lines
Credit Commitments
Credit commitments	99,666
Outside U.S. | Commercial and other consumer loan commitments
Credit Commitments
Credit commitments	101,272
Outside U.S. | Other commitments and contingencies
Credit Commitments
Credit commitments	$ 889