PLEDGED ASSETS, COLLATERAL, GUARANTEES AND COMMITMENTS - Credit Commitments and Lines of Credit (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Credit Commitments
Credit commitments	$ 1,066,364	$ 1,030,242
Unsettled reverse repurchase and securities borrowing agreements	34,000	36,100
Unsettled repurchase and securities lending agreements	38,700	30,700
Commercial and similar letters of credit
Credit Commitments
Credit commitments	4,533	5,461
One-to four-family residential mortgages
Credit Commitments
Credit commitments	3,721	2,671
Revolving open-end loans secured by one-to four-family residential properties
Credit Commitments
Credit commitments	10,799	11,374
Commercial real estate, construction and land development
Credit Commitments
Credit commitments	12,981	11,293
Credit card lines
Credit Commitments
Credit commitments	708,023	696,007
Commercial and other consumer loan commitments
Credit Commitments
Credit commitments	324,359	300,115
Other commitments and contingencies
Credit Commitments
Credit commitments	1,948	$ 3,321
U.S.
Credit Commitments
Credit commitments	847,255
U.S. | Commercial and similar letters of credit
Credit Commitments
Credit commitments	746
U.S. | One-to four-family residential mortgages
Credit Commitments
Credit commitments	2,088
U.S. | Revolving open-end loans secured by one-to four-family residential properties
Credit Commitments
Credit commitments	9,511
U.S. | Commercial real estate, construction and land development
Credit Commitments
Credit commitments	10,623
U.S. | Credit card lines
Credit Commitments
Credit commitments	609,866
U.S. | Commercial and other consumer loan commitments
Credit Commitments
Credit commitments	212,569
U.S. | Other commitments and contingencies
Credit Commitments
Credit commitments	1,852
Outside U.S.
Credit Commitments
Credit commitments	219,109
Outside U.S. | Commercial and similar letters of credit
Credit Commitments
Credit commitments	3,787
Outside U.S. | One-to four-family residential mortgages
Credit Commitments
Credit commitments	1,633
Outside U.S. | Revolving open-end loans secured by one-to four-family residential properties
Credit Commitments
Credit commitments	1,288
Outside U.S. | Commercial real estate, construction and land development
Credit Commitments
Credit commitments	2,358
Outside U.S. | Credit card lines
Credit Commitments
Credit commitments	98,157
Outside U.S. | Commercial and other consumer loan commitments
Credit Commitments
Credit commitments	111,790
Outside U.S. | Other commitments and contingencies
Credit Commitments
Credit commitments	$ 96