GUARANTEES, LEASES AND COMMITMENTS - Credit Commitments and Lines of Credit (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Guarantor Obligations
Credit commitments	$ 1,084,183	$ 1,071,288
Unsettled reverse repurchase and securities borrowing agreements	92,400	71,800
Unsettled repurchase and securities lending agreements	38,200	62,500
Commercial and similar letters of credit
Guarantor Obligations
Credit commitments	5,769	5,221
One- to four-family residential mortgages
Guarantor Obligations
Credit commitments	4,343	5,002
Revolving open-end loans secured by one- to four-family residential properties
Guarantor Obligations
Credit commitments	8,841	9,626
Commercial real estate, construction and land development
Guarantor Obligations
Credit commitments	16,466	12,867
Credit card lines
Guarantor Obligations
Credit commitments	707,951	710,399
Commercial and other consumer loan commitments
Guarantor Obligations
Credit commitments	335,011	322,458
Other commitments and contingencies
Guarantor Obligations
Credit commitments	5,802	$ 5,715
U.S.
Guarantor Obligations
Credit commitments	850,643
U.S. | Commercial and similar letters of credit
Guarantor Obligations
Credit commitments	929
U.S. | One- to four-family residential mortgages
Guarantor Obligations
Credit commitments	1,823
U.S. | Revolving open-end loans secured by one- to four-family residential properties
Guarantor Obligations
Credit commitments	7,687
U.S. | Commercial real estate, construction and land development
Guarantor Obligations
Credit commitments	14,959
U.S. | Credit card lines
Guarantor Obligations
Credit commitments	605,944
U.S. | Commercial and other consumer loan commitments
Guarantor Obligations
Credit commitments	214,023
U.S. | Other commitments and contingencies
Guarantor Obligations
Credit commitments	5,278
Outside of  U.S.
Guarantor Obligations
Credit commitments	233,540
Outside of  U.S. | Commercial and similar letters of credit
Guarantor Obligations
Credit commitments	4,840
Outside of  U.S. | One- to four-family residential mortgages
Guarantor Obligations
Credit commitments	2,520
Outside of  U.S. | Revolving open-end loans secured by one- to four-family residential properties
Guarantor Obligations
Credit commitments	1,154
Outside of  U.S. | Commercial real estate, construction and land development
Guarantor Obligations
Credit commitments	1,507
Outside of  U.S. | Credit card lines
Guarantor Obligations
Credit commitments	102,007
Outside of  U.S. | Commercial and other consumer loan commitments
Guarantor Obligations
Credit commitments	120,988
Outside of  U.S. | Other commitments and contingencies
Guarantor Obligations
Credit commitments	$ 524