GUARANTEES AND COMMITMENTS - Credit Commitments and Lines of Credit (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Guarantor Obligations
Credit commitments	$ 979,044	$ 960,231
Unsettled reverse repurchase and securities borrowing agreements	44,800	43,100
Unsettled repurchase and securities lending agreements	23,900	14,900
Commercial and similar letters of credit
Guarantor Obligations
Credit commitments	5,053	5,736
One- to four-family residential mortgages
Guarantor Obligations
Credit commitments	3,183	2,838
Revolving open-end loans secured by one- to four-family residential properties
Guarantor Obligations
Credit commitments	12,645	13,405
Commercial real estate, construction and land development
Guarantor Obligations
Credit commitments	11,139	10,781
Credit card lines
Guarantor Obligations
Credit commitments	679,909	664,335
Commercial and other consumer loan commitments
Guarantor Obligations
Credit commitments	263,675	259,934
Other commitments and contingencies
Guarantor Obligations
Credit commitments	3,440	$ 3,202
U.S.
Guarantor Obligations
Credit commitments	771,547
U.S. | Commercial and similar letters of credit
Guarantor Obligations
Credit commitments	756
U.S. | One- to four-family residential mortgages
Guarantor Obligations
Credit commitments	1,352
U.S. | Revolving open-end loans secured by one- to four-family residential properties
Guarantor Obligations
Credit commitments	11,137
U.S. | Commercial real estate, construction and land development
Guarantor Obligations
Credit commitments	9,166
U.S. | Credit card lines
Guarantor Obligations
Credit commitments	579,285
U.S. | Commercial and other consumer loan commitments
Guarantor Obligations
Credit commitments	167,736
U.S. | Other commitments and contingencies
Guarantor Obligations
Credit commitments	2,115
Outside of U.S.
Guarantor Obligations
Credit commitments	207,497
Outside of U.S. | Commercial and similar letters of credit
Guarantor Obligations
Credit commitments	4,297
Outside of U.S. | One- to four-family residential mortgages
Guarantor Obligations
Credit commitments	1,831
Outside of U.S. | Revolving open-end loans secured by one- to four-family residential properties
Guarantor Obligations
Credit commitments	1,508
Outside of U.S. | Commercial real estate, construction and land development
Guarantor Obligations
Credit commitments	1,973
Outside of U.S. | Credit card lines
Guarantor Obligations
Credit commitments	100,624
Outside of U.S. | Commercial and other consumer loan commitments
Guarantor Obligations
Credit commitments	95,939
Outside of U.S. | Other commitments and contingencies
Guarantor Obligations
Credit commitments	$ 1,325