Quarterly report pursuant to Section 13 or 15(d)

HELD-TO-MATURITY SECURITIES - Amortized Cost, Gross Unrealized Gains and Losses, & Fair Value (Details)

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HELD-TO-MATURITY SECURITIES - Amortized Cost, Gross Unrealized Gains and Losses, & Fair Value (Details) - USD ($)
$ in Millions
Jun. 30, 2018
Dec. 31, 2017
Schedule of Held-to-maturity Securities [Line Items]    
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value $ 8,298 $ 8,464
Amortized Cost 8,682 9,091
Unrealized Gross Gains 0 4
Unrealized Gross Losses (291) (124)
Fair Value 8,391 8,971
Collateralized Mortgage Obligations [Member]    
Schedule of Held-to-maturity Securities [Line Items]    
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value 2,222 3,388
Amortized Cost 2,299 3,714
Unrealized Gross Gains 0 1
Unrealized Gross Losses (77) (58)
Fair Value 2,222 3,657
Residential Mortgage Backed Securities [Member]    
Schedule of Held-to-maturity Securities [Line Items]    
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value 1,552 974
Amortized Cost 1,677 1,049
Unrealized Gross Gains 0 2
Unrealized Gross Losses (54) (7)
Fair Value 1,623 1,044
Commercial Mortgage Backed Securities [Member]    
Schedule of Held-to-maturity Securities [Line Items]    
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value 4,174 3,709
Amortized Cost 4,326 3,791
Unrealized Gross Gains 0 0
Unrealized Gross Losses (152) (55)
Fair Value 4,174 3,736
Federal agencies, Other agencies    
Schedule of Held-to-maturity Securities [Line Items]    
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value 345 388
Amortized Cost 375 532
Unrealized Gross Gains 0 1
Unrealized Gross Losses (8) (4)
Fair Value 367 529
Total U.S. Treasury, Federal agency and other agency securities    
Schedule of Held-to-maturity Securities [Line Items]    
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value 8,293 8,459
Amortized Cost 8,677 9,086
Unrealized Gross Gains 0 4
Unrealized Gross Losses (291) (124)
Fair Value 8,386 8,966
Municipal securities    
Schedule of Held-to-maturity Securities [Line Items]    
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value 5 5
Amortized Cost 5 5
Unrealized Gross Gains 0 0
Unrealized Gross Losses 0 0
Fair Value $ 5 $ 5