GUARANTEES, LEASES AND COMMITMENTS - Credit Commitments and Lines of Credit (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Guarantor Obligations
Credit commitments	$ 1,049,446	$ 1,030,242
Unsettled reverse repurchase and securities borrowing agreements	64,900	36,100
Unsettled repurchase and securities lending agreements	55,300	30,700
Commercial and similar letters of credit
Guarantor Obligations
Credit commitments	5,895	5,461
One- to four-family residential mortgages
Guarantor Obligations
Credit commitments	3,419	2,671
Revolving open-end loans secured by one- to four-family residential properties
Guarantor Obligations
Credit commitments	11,312	11,374
Commercial real estate, construction and land development
Guarantor Obligations
Credit commitments	11,436	11,293
Credit card lines
Guarantor Obligations
Credit commitments	708,095	696,007
Commercial and other consumer loan commitments
Guarantor Obligations
Credit commitments	306,342	300,115
Other commitments and contingencies
Guarantor Obligations
Credit commitments	2,947	$ 3,321
U.S.
Guarantor Obligations
Credit commitments	834,262
U.S. | Commercial and similar letters of credit
Guarantor Obligations
Credit commitments	834
U.S. | One- to four-family residential mortgages
Guarantor Obligations
Credit commitments	1,750
U.S. | Revolving open-end loans secured by one- to four-family residential properties
Guarantor Obligations
Credit commitments	9,977
U.S. | Commercial real estate, construction and land development
Guarantor Obligations
Credit commitments	9,798
U.S. | Credit card lines
Guarantor Obligations
Credit commitments	615,230
U.S. | Commercial and other consumer loan commitments
Guarantor Obligations
Credit commitments	194,289
U.S. | Other commitments and contingencies
Guarantor Obligations
Credit commitments	2,384
Outside of U.S.
Guarantor Obligations
Credit commitments	215,184
Outside of U.S. | Commercial and similar letters of credit
Guarantor Obligations
Credit commitments	5,061
Outside of U.S. | One- to four-family residential mortgages
Guarantor Obligations
Credit commitments	1,669
Outside of U.S. | Revolving open-end loans secured by one- to four-family residential properties
Guarantor Obligations
Credit commitments	1,335
Outside of U.S. | Commercial real estate, construction and land development
Guarantor Obligations
Credit commitments	1,638
Outside of U.S. | Credit card lines
Guarantor Obligations
Credit commitments	92,865
Outside of U.S. | Commercial and other consumer loan commitments
Guarantor Obligations
Credit commitments	112,053
Outside of U.S. | Other commitments and contingencies
Guarantor Obligations
Credit commitments	$ 563