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SECURITIES - Fair Values and Unrealized Losses of Impaired Securities, by Length of Impairment (Detail) $ in Millions | Jun. 30, 2019 USD ($) Security | Dec. 31, 2018 USD ($) Security
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Schedule Of Securities [Line Items] |  |
Number of available for sale securities, Less than 1 year | Security | 5 | 46
Number of available for sale securities, Greater than 1 year | Security | 116 | 136
Number of available for sale securities | Security | 121 | 182
Securities available for sale, less than 12 months, fair value | $ 19 | $ 679
Securities available for sale, 12 months or more, fair value | 1,505 | 1,988
Securities available for sale, fair value, total | 1,524 | 2,667
Securities available for sale, less than 12 months, unrealized losses | 0 | (7)
Securities available for sale, 12 months or more, unrealized losses | (12) | (58)
Securities available for sale, unrealized losses, total | $ (12) | $ (65)
Number of securities held to maturity positions | Security | 130 | 373
Securities held to maturity, less than 12 months, fair value | $ 4 | $ 952
Securities held to maturity, greater than 12 months, fair value | 1,256 | 1,720
Securities held to maturity, fair value, total | 1,260 | 2,672
Securities held to maturity, less than 12 months, unrealized losses | 0 | (31)
Securities held to maturity, greater than 12 months, unrealized losses | (18) | (73)
Securities held to maturity, unrealized losses, total | $ (18) | $ (104)
Less Than Twelve Months [Member] |  |
Schedule Of Securities [Line Items] |  |
Number of securities held to maturity positions | Security | 1 | 210
Greater Than Twelve Months [Member] |  |
Schedule Of Securities [Line Items] |  |
Number of securities held to maturity positions | Security | 129 | 163
US Government Agencies [Member] |  |
Schedule Of Securities [Line Items] |  |
Number of available for sale securities, Less than 1 year | Security | 5 | 20
Number of available for sale securities, Greater than 1 year | Security | 12 | 0
Number of available for sale securities | Security | 17 | 20
Securities available for sale, less than 12 months, fair value | $ 19 | $ 145
Securities available for sale, 12 months or more, fair value | 74 | 0
Securities available for sale, fair value, total | 93 | 145
Securities available for sale, less than 12 months, unrealized losses | 0 | (1)
Securities available for sale, 12 months or more, unrealized losses | 0 | 0
Securities available for sale, unrealized losses, total | $ 0 | $ (1)
U.S. Government-Sponsored Entities [Member] |  |
Schedule Of Securities [Line Items] |  |
Number of available for sale securities, Less than 1 year | Security | 0 | 1
Number of available for sale securities, Greater than 1 year | Security | 9 | 11
Number of available for sale securities | Security | 9 | 12
Securities available for sale, less than 12 months, fair value | $ 0 | $ 36
Securities available for sale, 12 months or more, fair value | 205 | 227
Securities available for sale, fair value, total | 205 | 263
Securities available for sale, less than 12 months, unrealized losses | 0 | 0
Securities available for sale, 12 months or more, unrealized losses | (1) | (4)
Securities available for sale, unrealized losses, total | $ (1) | $ (4)
Number of securities held to maturity positions | Security | 10 | 12
Securities held to maturity, less than 12 months, fair value | $ 0 | $ 0
Securities held to maturity, greater than 12 months, fair value | 189 | 211
Securities held to maturity, fair value, total | 189 | 211
Securities held to maturity, less than 12 months, unrealized losses | 0 | 0
Securities held to maturity, greater than 12 months, unrealized losses | (1) | (4)
Securities held to maturity, unrealized losses, total | $ (1) | $ (4)
U.S. Government-Sponsored Entities [Member] | Less Than Twelve Months [Member] |  |
Schedule Of Securities [Line Items] |  |
Number of securities held to maturity positions | Security | 0 | 0
U.S. Government-Sponsored Entities [Member] | Greater Than Twelve Months [Member] |  |
Schedule Of Securities [Line Items] |  |
Number of securities held to maturity positions | Security | 10 | 12
Agency Mortgage-Backed Securities [Member] |  |
Schedule Of Securities [Line Items] |  |
Number of available for sale securities, Less than 1 year | Security | 0 | 16
Number of available for sale securities, Greater than 1 year | Security | 53 | 71
Number of available for sale securities | Security | 53 | 87
Securities available for sale, less than 12 months, fair value | $ 0 | $ 259
Securities available for sale, 12 months or more, fair value | 849 | 1,159
Securities available for sale, fair value, total | 849 | 1,418
Securities available for sale, less than 12 months, unrealized losses | 0 | (4)
Securities available for sale, 12 months or more, unrealized losses | (6) | (32)
Securities available for sale, unrealized losses, total | $ (6) | $ (36)
Number of securities held to maturity positions | Security | 36 | 90
Securities held to maturity, less than 12 months, fair value | $ 0 | $ 294
Securities held to maturity, greater than 12 months, fair value | 506 | 694
Securities held to maturity, fair value, total | 506 | 988
Securities held to maturity, less than 12 months, unrealized losses | 0 | (4)
Securities held to maturity, greater than 12 months, unrealized losses | (4) | (22)
Securities held to maturity, unrealized losses, total | $ (4) | $ (26)
Agency Mortgage-Backed Securities [Member] | Less Than Twelve Months [Member] |  |
Schedule Of Securities [Line Items] |  |
Number of securities held to maturity positions | Security | 0 | 43
Agency Mortgage-Backed Securities [Member] | Greater Than Twelve Months [Member] |  |
Schedule Of Securities [Line Items] |  |
Number of securities held to maturity positions | Security | 36 | 47
Agency Collateralized Mortgage Obligations [Member] |  |
Schedule Of Securities [Line Items] |  |
Number of available for sale securities, Less than 1 year | Security | 0 | 2
Number of available for sale securities, Greater than 1 year | Security | 38 | 47
Number of available for sale securities | Security | 38 | 49
Securities available for sale, less than 12 months, fair value | $ 0 | $ 82
Securities available for sale, 12 months or more, fair value | 370 | 590
Securities available for sale, fair value, total | 370 | 672
Securities available for sale, less than 12 months, unrealized losses | 0 | (1)
Securities available for sale, 12 months or more, unrealized losses | (5) | (22)
Securities available for sale, unrealized losses, total | $ (5) | $ (23)
Number of securities held to maturity positions | Security | 38 | 52
Securities held to maturity, less than 12 months, fair value | $ 0 | $ 42
Securities held to maturity, greater than 12 months, fair value | 381 | 611
Securities held to maturity, fair value, total | 381 | 653
Securities held to maturity, less than 12 months, unrealized losses | 0 | 0
Securities held to maturity, greater than 12 months, unrealized losses | (8) | (24)
Securities held to maturity, unrealized losses, total | $ (8) | $ (24)
Agency Collateralized Mortgage Obligations [Member] | Less Than Twelve Months [Member] |  |
Schedule Of Securities [Line Items] |  |
Number of securities held to maturity positions | Security | 0 | 3
Agency Collateralized Mortgage Obligations [Member] | Greater Than Twelve Months [Member] |  |
Schedule Of Securities [Line Items] |  |
Number of securities held to maturity positions | Security | 38 | 49
Non Agency Collateralized Mortgage Obligations [Member] |  |
Schedule Of Securities [Line Items] |  |
Number of available for sale securities, Less than 1 year | Security |  | 1
Number of available for sale securities, Greater than 1 year | Security |  | 0
Number of available for sale securities | Security |  | 1
Securities available for sale, less than 12 months, fair value |  | $ 0
Securities available for sale, 12 months or more, fair value |  | 0
Securities available for sale, fair value, total |  | 0
Securities available for sale, less than 12 months, unrealized losses |  | 0
Securities available for sale, 12 months or more, unrealized losses |  | 0
Securities available for sale, unrealized losses, total |  | $ 0
Commercial Mortgage-Backed Securities [Member] |  |
Schedule Of Securities [Line Items] |  |
Number of available for sale securities, Less than 1 year | Security |  | 4
Number of available for sale securities, Greater than 1 year | Security |  | 0
Number of available for sale securities | Security |  | 4
Securities available for sale, less than 12 months, fair value |  | $ 155
Securities available for sale, 12 months or more, fair value |  | 0
Securities available for sale, fair value, total |  | 155
Securities available for sale, less than 12 months, unrealized losses |  | (1)
Securities available for sale, 12 months or more, unrealized losses |  | 0
Securities available for sale, unrealized losses, total |  | $ (1)
Number of securities held to maturity positions | Security | 2 | 9
Securities held to maturity, less than 12 months, fair value | $ 0 | $ 26
Securities held to maturity, greater than 12 months, fair value | 9 | 43
Securities held to maturity, fair value, total | 9 | 69
Securities held to maturity, less than 12 months, unrealized losses | 0 | 0
Securities held to maturity, greater than 12 months, unrealized losses | 0 | (1)
Securities held to maturity, unrealized losses, total | $ 0 | $ (1)
Commercial Mortgage-Backed Securities [Member] | Less Than Twelve Months [Member] |  |
Schedule Of Securities [Line Items] |  |
Number of securities held to maturity positions | Security | 0 | 5
Commercial Mortgage-Backed Securities [Member] | Greater Than Twelve Months [Member] |  |
Schedule Of Securities [Line Items] |  |
Number of securities held to maturity positions | Security | 2 | 4
States of the U.S. and Political Subdivisions [Member] |  |
Schedule Of Securities [Line Items] |  |
Number of available for sale securities, Less than 1 year | Security | 0 | 2
Number of available for sale securities, Greater than 1 year | Security | 3 | 6
Number of available for sale securities | Security | 3 | 8
Securities available for sale, less than 12 months, fair value | $ 0 | $ 2
Securities available for sale, 12 months or more, fair value | 5 | 10
Securities available for sale, fair value, total | 5 | 12
Securities available for sale, less than 12 months, unrealized losses | 0 | 0
Securities available for sale, 12 months or more, unrealized losses | 0 | 0
Securities available for sale, unrealized losses, total | $ 0 | $ 0
Number of securities held to maturity positions | Security | 44 | 210
Securities held to maturity, less than 12 months, fair value | $ 4 | $ 590
Securities held to maturity, greater than 12 months, fair value | 171 | 161
Securities held to maturity, fair value, total | 175 | 751
Securities held to maturity, less than 12 months, unrealized losses | 0 | (27)
Securities held to maturity, greater than 12 months, unrealized losses | (5) | (22)
Securities held to maturity, unrealized losses, total | $ (5) | $ (49)
States of the U.S. and Political Subdivisions [Member] | Less Than Twelve Months [Member] |  |
Schedule Of Securities [Line Items] |  |
Number of securities held to maturity positions | Security | 1 | 159
States of the U.S. and Political Subdivisions [Member] | Greater Than Twelve Months [Member] |  |
Schedule Of Securities [Line Items] |  |
Number of securities held to maturity positions | Security | 43 | 51
Other Debt Securities [Member] |  |
Schedule Of Securities [Line Items] |  |
Number of available for sale securities, Less than 1 year | Security | 0 | 0
Number of available for sale securities, Greater than 1 year | Security | 1 | 1
Number of available for sale securities | Security | 1 | 1
Securities available for sale, less than 12 months, fair value | $ 0 | $ 0
Securities available for sale, 12 months or more, fair value | 2 | 2
Securities available for sale, fair value, total | 2 | 2
Securities available for sale, less than 12 months, unrealized losses | 0 | 0
Securities available for sale, 12 months or more, unrealized losses | 0 | 0
Securities available for sale, unrealized losses, total | $ 0 | $ 0

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