Quarterly report pursuant to Section 13 or 15(d)

HELD-TO-MATURITY SECURITIES - Contractual Maturities (Details)

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HELD-TO-MATURITY SECURITIES - Contractual Maturities (Details) - USD ($)
$ in Millions
Mar. 31, 2018
Dec. 31, 2017
Schedule of Held-to-maturity Securities [Line Items]    
Over 12 Months $ 2,106 $ 1,416
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount [Abstract]    
Amortized Cost 8,789 9,091
Held-to-maturity Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]    
Fair Value 8,549 8,971
Collateralized Mortgage Obligations [Member]    
Schedule of Held-to-maturity Securities [Line Items]    
Over 12 Months 1,313 1,019
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount [Abstract]    
Held-to-maturity Securities, 6-10 years 39 0
Held-to-maturity Securities, Over 10 years 2,354 3,714
Amortized Cost 2,393 3,714
Held-to-maturity Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]    
Fair Value, 6-10 years 38 0
Fair Value, Over 10 years 2,291 3,657
Fair Value 2,329 3,657
Residential Mortgage Backed Securities [Member]    
Schedule of Held-to-maturity Securities [Line Items]    
Over 12 Months 0 0
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount [Abstract]    
Held-to-maturity Securities, 6-10 years 0 28
Held-to-maturity Securities, Over 10 years 1,651 1,021
Amortized Cost 1,651 1,049
Held-to-maturity Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]    
Fair Value, 6-10 years 0 28
Fair Value, Over 10 years 1,606 1,016
Fair Value 1,606 1,044
Commercial Mortgage Backed Securities [Member]    
Schedule of Held-to-maturity Securities [Line Items]    
Over 12 Months 726 253
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount [Abstract]    
Held-to-maturity Securities, 1-5 years 0 38
Held-to-maturity Securities, 6-10 years 131 1
Held-to-maturity Securities, Over 10 years 4,223 3,752
Amortized Cost 4,354 3,791
Held-to-maturity Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]    
Fair Value, 1-5 years 0 37
Fair Value, 6-10 years 128 1
Fair Value, Over 10 years 4,101 3,698
Fair Value 4,229 3,736
Federal agencies, Other agencies    
Schedule of Held-to-maturity Securities [Line Items]    
Over 12 Months 62 139
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount [Abstract]    
Held-to-maturity Securities, 1-5 years 14 7
Held-to-maturity Securities, 6-10 years 215 362
Held-to-maturity Securities, Over 10 years 157 163
Amortized Cost 386 532
Held-to-maturity Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]    
Fair Value, 1-5 years 13 8
Fair Value, 6-10 years 213 360
Fair Value, Over 10 years 154 161
Fair Value 380 529
Total U.S. Treasury, Federal agency and other agency securities    
Schedule of Held-to-maturity Securities [Line Items]    
Over 12 Months 2,101 1,411
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount [Abstract]    
Amortized Cost 8,784 9,086
Held-to-maturity Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]    
Fair Value 8,544 8,966
Municipal securities    
Schedule of Held-to-maturity Securities [Line Items]    
Over 12 Months 5 5
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount [Abstract]    
Held-to-maturity Securities, Over 10 years 5 5
Amortized Cost 5 5
Held-to-maturity Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]    
Fair Value, Over 10 years 5 5
Fair Value $ 5 $ 5