GUARANTEES, LEASES AND COMMITMENTS - Credit Commitments and Lines of Credit (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Guarantor Obligations
Credit commitments	$ 1,079,659	$ 1,071,288
Unsettled reverse repurchase and securities borrowing agreements	135,800	71,800
Unsettled repurchase and securities lending agreements	57,400	62,500
Commercial and similar letters of credit
Guarantor Obligations
Credit commitments	6,409	5,221
One- to four-family residential mortgages
Guarantor Obligations
Credit commitments	4,491	5,002
Revolving open-end loans secured by one- to four-family residential properties
Guarantor Obligations
Credit commitments	8,355	9,626
Commercial real estate, construction and land development
Guarantor Obligations
Credit commitments	17,000	12,867
Credit card lines
Guarantor Obligations
Credit commitments	704,957	710,399
Commercial and other consumer loan commitments
Guarantor Obligations
Credit commitments	332,798	322,458
Other commitments and contingencies
Guarantor Obligations
Credit commitments	5,649	$ 5,715
U.S.
Guarantor Obligations
Credit commitments	848,225
U.S. | Commercial and similar letters of credit
Guarantor Obligations
Credit commitments	696
U.S. | One- to four-family residential mortgages
Guarantor Obligations
Credit commitments	1,735
U.S. | Revolving open-end loans secured by one- to four-family residential properties
Guarantor Obligations
Credit commitments	7,225
U.S. | Commercial real estate, construction and land development
Guarantor Obligations
Credit commitments	14,267
U.S. | Credit card lines
Guarantor Obligations
Credit commitments	604,350
U.S. | Commercial and other consumer loan commitments
Guarantor Obligations
Credit commitments	214,515
U.S. | Other commitments and contingencies
Guarantor Obligations
Credit commitments	5,437
Outside of  U.S.
Guarantor Obligations
Credit commitments	231,434
Outside of  U.S. | Commercial and similar letters of credit
Guarantor Obligations
Credit commitments	5,713
Outside of  U.S. | One- to four-family residential mortgages
Guarantor Obligations
Credit commitments	2,756
Outside of  U.S. | Revolving open-end loans secured by one- to four-family residential properties
Guarantor Obligations
Credit commitments	1,130
Outside of  U.S. | Commercial real estate, construction and land development
Guarantor Obligations
Credit commitments	2,733
Outside of  U.S. | Credit card lines
Guarantor Obligations
Credit commitments	100,607
Outside of  U.S. | Commercial and other consumer loan commitments
Guarantor Obligations
Credit commitments	118,283
Outside of  U.S. | Other commitments and contingencies
Guarantor Obligations
Credit commitments	$ 212