| **INVESTMENT SECURITIES (Gross Unrealized Loss and Fair Value of Securities Available for Sale) (Details) - USD ($) $ in Thousands** | Jun. 30, 2016 | Dec. 31, 2015 |
|--------------------------------------------------------------------------------------------------------------------------------------|---------------|---------------|
| **Fair Value**                                                                                                                       |          |          |
| Less than 12 months                                                                                                                  | $ 1,473,360   | $ 10,139,369  |
| 12 months or longer                                                                                                                  | 2,849,625     | 3,420,300     |
| Total                                                                                                                                | 4,322,985     | 13,559,669    |
| **Unrealized Losses**                                                                                                                |          |          |
| Less than 12 months                                                                                                                  | (7,733)       | (67,205)      |
| 12 months or longer                                                                                                                  | (42,938)      | (151,339)     |
| Total                                                                                                                                | (50,671)      | (218,544)     |
| U.S. Treasury securities                                                                                                             |          |          |
| **Fair Value**                                                                                                                       |          |          |
| Less than 12 months                                                                                                                  |          | 2,243,343     |
| 12 months or longer                                                                                                                  |          | 0             |
| Total                                                                                                                                |          | 2,243,343     |
| **Unrealized Losses**                                                                                                                |          |          |
| Less than 12 months                                                                                                                  |          | (5,681)       |
| 12 months or longer                                                                                                                  |          | 0             |
| Total                                                                                                                                | 0             | (5,681)       |
| Corporate debt securities                                                                                                            |          |          |
| **Fair Value**                                                                                                                       |          |          |
| Less than 12 months                                                                                                                  |          | 775,366       |
| 12 months or longer                                                                                                                  |          | 152,486       |
| Total                                                                                                                                |          | 927,852       |
| **Unrealized Losses**                                                                                                                |          |          |
| Less than 12 months                                                                                                                  |          | (5,269)       |
| 12 months or longer                                                                                                                  |          | (5,979)       |
| Total                                                                                                                                |          | (11,248)      |
| Asset-backed securities                                                                                                              |          |          |
| **Fair Value**                                                                                                                       |          |          |
| Less than 12 months                                                                                                                  | 346,390       | 300,869       |
| 12 months or longer                                                                                                                  | 60,299        | 35,126        |
| Total                                                                                                                                | 406,689       | 335,995       |
| **Unrealized Losses**                                                                                                                |          |          |
| Less than 12 months                                                                                                                  | (766)         | (1,083)       |
| 12 months or longer                                                                                                                  | (864)         | (411)         |
| Total                                                                                                                                | (1,630)       | (1,494)       |
| Equity securities                                                                                                                    |          |          |
| **Fair Value**                                                                                                                       |          |          |
| Less than 12 months                                                                                                                  | 0             | 596           |
| 12 months or longer                                                                                                                  | 10,112        | 9,748         |
| Total                                                                                                                                | 10,112        | 10,344        |
| **Unrealized Losses**                                                                                                                |          |          |
| Less than 12 months                                                                                                                  | 0             | (7)           |
| 12 months or longer                                                                                                                  | (238)         | (401)         |
| Total                                                                                                                                | (238)         | (408)         |
| State and municipal securities                                                                                                       |          |          |
| **Fair Value**                                                                                                                       |          |          |
| Less than 12 months                                                                                                                  |          | 15,665        |
| 12 months or longer                                                                                                                  |          | 26,024        |
| Total                                                                                                                                |          | 41,689        |
| **Unrealized Losses**                                                                                                                |          |          |
| Less than 12 months                                                                                                                  |          | (119)         |
| 12 months or longer                                                                                                                  |          | (313)         |
| Total                                                                                                                                | 0             | (432)         |
| U.S. government agencies - Residential                                                                                               |          |          |
| **Fair Value**                                                                                                                       |          |          |
| Less than 12 months                                                                                                                  | 954,360       | 1,670,150     |
| 12 months or longer                                                                                                                  | 589,955       | 954,916       |
| Total                                                                                                                                | 1,544,315     | 2,625,066     |
| **Unrealized Losses**                                                                                                                |          |          |
| Less than 12 months                                                                                                                  | (6,538)       | (11,164)      |
| 12 months or longer                                                                                                                  | (3,342)       | (25,349)      |
| Total                                                                                                                                | (9,880)       | (36,513)      |
| U.S. government agencies - Commercial                                                                                                |          |          |
| **Fair Value**                                                                                                                       |          |          |
| Less than 12 months                                                                                                                  | 0             | 367,706       |
| 12 months or longer                                                                                                                  | 112,214       | 114,038       |
| Total                                                                                                                                | 112,214       | 481,744       |
| **Unrealized Losses**                                                                                                                |          |          |
| Less than 12 months                                                                                                                  | 0             | (3,382)       |
| 12 months or longer                                                                                                                  | (1,295)       | (3,771)       |
| Total                                                                                                                                | (1,295)       | (7,153)       |
| FHLMC and FNMA - Residential debt securities                                                                                         |          |          |
| **Fair Value**                                                                                                                       |          |          |
| Less than 12 months                                                                                                                  | 172,139       | 4,650,327     |
| 12 months or longer                                                                                                                  | 2,077,045     | 2,127,962     |
| Total                                                                                                                                | 2,249,184     | 6,778,289     |
| **Unrealized Losses**                                                                                                                |          |          |
| Less than 12 months                                                                                                                  | (421)         | (38,013)      |
| 12 months or longer                                                                                                                  | (37,199)      | (115,115)     |
| Total                                                                                                                                | (37,620)      | (153,128)     |
| FHLMC and FNMA - Commercial debt securities                                                                                          |          |          |
| **Fair Value**                                                                                                                       |          |          |
| Less than 12 months                                                                                                                  | 471           | 115,347       |
| 12 months or longer                                                                                                                  | 0             | 0             |
| Total                                                                                                                                | 471           | 115,347       |
| **Unrealized Losses**                                                                                                                |          |          |
| Less than 12 months                                                                                                                  | (8)           | (2,487)       |
| 12 months or longer                                                                                                                  | 0             | 0             |
| Total                                                                                                                                | $ (8)         | $ (2,487)     |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - 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.
+ References
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|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for twelve months or longer.
+ References
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| - Definition
This item represents the aggregate fair value of investments in debt and equity securities in an unrealized loss position which are categorized neither as held-to-maturity nor trading securities.
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|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for less than twelve months.
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This item represents the aggregate fair value of investments in debt and equity securities categorized neither as held-to-maturity nor trading securities that have been in a continuous unrealized loss position for less than twelve months.
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