| **INVESTMENT SECURITIES (Available-for-sale Securities) (Details) - USD ($) $ in Thousands** | Mar. 31, 2016 | Dec. 31, 2015 |
|----------------------------------------------------------------------------------------------|---------------|---------------|
| **Schedule of Available-for-sale Securities [Line Items]**                                   |          |          |
| Amortized Cost                                                                               | $ 20,440,266  | $ 21,006,066  |
| Gross Unrealized Gains                                                                       | 178,967       | 63,973        |
| Gross Unrealized Loss                                                                        | (86,117)      | (218,544)     |
| Fair Value                                                                                   | 20,533,116    | 20,851,495    |
| Accrued investment income receivable                                                         | 54,900        | 65,100        |
| U.S. Treasury securities                                                                     |          |          |
| **Schedule of Available-for-sale Securities [Line Items]**                                   |          |          |
| Amortized Cost                                                                               | 349,274       | 3,192,411     |
| Gross Unrealized Gains                                                                       | 468           | 1,658         |
| Gross Unrealized Loss                                                                        | 0             | (5,681)       |
| Fair Value                                                                                   | 349,742       | 3,188,388     |
| Corporate debt securities                                                                    |          |          |
| **Schedule of Available-for-sale Securities [Line Items]**                                   |          |          |
| Amortized Cost                                                                               | 1,417,264     | 1,476,801     |
| Gross Unrealized Gains                                                                       | 15,972        | 10,021        |
| Gross Unrealized Loss                                                                        | (3,646)       | (11,248)      |
| Fair Value                                                                                   | 1,429,590     | 1,475,574     |
| Asset-backed securities (ABS)                                                                |          |          |
| **Schedule of Available-for-sale Securities [Line Items]**                                   |          |          |
| Amortized Cost                                                                               | 2,038,606     | 1,763,178     |
| Gross Unrealized Gains                                                                       | 9,621         | 7,826         |
| Gross Unrealized Loss                                                                        | (1,648)       | (1,494)       |
| Fair Value                                                                                   | 2,046,579     | 1,769,510     |
| Equity securities                                                                            |          |          |
| **Schedule of Available-for-sale Securities [Line Items]**                                   |          |          |
| Amortized Cost                                                                               | 10,964        | 10,894        |
| Gross Unrealized Gains                                                                       | 5             | 1             |
| Gross Unrealized Loss                                                                        | (282)         | (408)         |
| Fair Value                                                                                   | 10,687        | 10,487        |
| State and municipal securities                                                               |          |          |
| **Schedule of Available-for-sale Securities [Line Items]**                                   |          |          |
| Amortized Cost                                                                               | 21,278        | 748,696       |
| Gross Unrealized Gains                                                                       | 349           | 19,616        |
| Gross Unrealized Loss                                                                        | 0             | (432)         |
| Fair Value                                                                                   | 21,627        | 767,880       |
| U.S. government agencies - Residential                                                       |          |          |
| **Schedule of Available-for-sale Securities [Line Items]**                                   |          |          |
| Amortized Cost                                                                               | 5,871,610     | 4,033,041     |
| Gross Unrealized Gains                                                                       | 51,967        | 10,225        |
| Gross Unrealized Loss                                                                        | (18,121)      | (36,513)      |
| Fair Value                                                                                   | 5,905,456     | 4,006,753     |
| U.S. government agencies - Commercial                                                        |          |          |
| **Schedule of Available-for-sale Securities [Line Items]**                                   |          |          |
| Amortized Cost                                                                               | 1,094,751     | 1,006,161     |
| Gross Unrealized Gains                                                                       | 16,994        | 3,347         |
| Gross Unrealized Loss                                                                        | (1,992)       | (7,153)       |
| Fair Value                                                                                   | 1,109,753     | 1,002,355     |
| FHLMC and FNMA - Residential debt securities                                                 |          |          |
| **Schedule of Available-for-sale Securities [Line Items]**                                   |          |          |
| Amortized Cost                                                                               | 9,498,678     | 8,636,745     |
| Gross Unrealized Gains                                                                       | 80,842        | 10,556        |
| Gross Unrealized Loss                                                                        | (60,101)      | (153,128)     |
| Fair Value                                                                                   | 9,519,419     | 8,494,173     |
| FHLMC and FNMA - Commercial debt securities                                                  |          |          |
| **Schedule of Available-for-sale Securities [Line Items]**                                   |          |          |
| Amortized Cost                                                                               | 137,804       | 138,094       |
| Gross Unrealized Gains                                                                       | 2,749         | 723           |
| Gross Unrealized Loss                                                                        | (327)         | (2,487)       |
| Fair Value                                                                                   | 140,226       | 136,330       |
| Non-agency securities                                                                        |          |          |
| **Schedule of Available-for-sale Securities [Line Items]**                                   |          |          |
| Amortized Cost                                                                               | 37            | 45            |
| Gross Unrealized Gains                                                                       | 0             | 0             |
| Gross Unrealized Loss                                                                        | 0             | 0             |
| Fair Value                                                                                   | $ 37          | $ 45          |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Interest, dividends, rents, ancillary and other revenues earned but not yet received by the entity on its investments.
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| - Definition
Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.
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| - Definition
Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.
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| - Definition
Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.
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| - Definition
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| - Definition
Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.
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No definition available.
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