| **ACCUMULATED OTHER COMPREHENSIVE INCOME / (LOSS) (Details) - USD ($) $ in Thousands**                     | 3 Months Ended | 9 Months Ended |
|------------------------------------------------------------------------------------------------------------|----------------|----------------|
||
| **Accumulated Other Comprehensive Income (Loss) [Line Items]**                                             |           |           |   |   |   |
| Total other comprehensive income/(loss), pretax activity                                                   | $ (73,961)     |           | $ 9,461 | $ (260,248) | $ 73,789 |
| Total other comprehensive income/(loss), tax effect                                                        | 20,420         |           | (2,858) | 34,783 | (25,791) |
| TOTAL OTHER COMPREHENSIVE (LOSS) / GAIN, NET OF TAX                                                        | (53,541)       |           | 6,603 | (225,465) | 47,998 |
| **AOCI Attributable to Parent, Net of Tax [Roll Forward]**                                                 |           |           |   |   |   |
| Equity, Beginning balance                                                                                  | 24,140,381     | $ 23,690,832   | 22,885,940 | 23,690,832 | 22,378,758 |
| Net Activity                                                                                               | (53,541)       |           | 6,603 | (225,465) | 47,998 |
| Net Activity, upon adoption                                                                                |           |           |   | (264,559) |   |
| Equity, Ending balance                                                                                     | 23,730,899     | 23,830,598     | 23,457,668 | 23,730,899 | 23,457,668 |
| Net unrealized (losses) on cash flow hedge derivative financial instruments                                |           |           |   |   |   |
| **Accumulated Other Comprehensive Income (Loss) [Line Items]**                                             |           |           |   |   |   |
| Other comprehensive income/(loss), pretax activity                                                         | (7,485)        |           | 5,298 | (42,590) | 12,469 |
| Other comprehensive income/(loss), tax effect                                                              | 4,052          |           | (955) | 6,542 | (2,950) |
| Other comprehensive income/(loss), net activity                                                            | (3,433)        |           | 4,343 | (36,048) | 9,519 |
| Reclassification adjustment, pretax activity                                                               | (567)          |           | (6,837) | 14,765 | (8,315) |
| Reclassification adjustment, tax effect                                                                    | 178            |           | 2,002 | (4,643) | 2,340 |
| Reclassification adjustment, net activity                                                                  | 389            |           | 4,835 | (10,122) | 5,975 |
| Total other comprehensive income/(loss), pretax activity                                                   | (8,052)        |           | (1,539) | (27,825) | 4,154 |
| Total other comprehensive income/(loss), tax effect                                                        | 4,230          |           | 1,047 | 1,899 | (610) |
| TOTAL OTHER COMPREHENSIVE (LOSS) / GAIN, NET OF TAX                                                        | (3,822)        |           | (492) | (25,926) | 3,544 |
| **AOCI Attributable to Parent, Net of Tax [Roll Forward]**                                                 |           |           |   |   |   |
| Equity, Beginning balance                                                                                  | (28,492)       | (6,388)        | (2,689) | (6,388) | (6,725) |
| Net Activity                                                                                               | (3,822)        |           | (492) | (25,926) | 3,544 |
| Equity, Ending balance                                                                                     | (32,314)       |           | (3,181) | (32,314) | (3,181) |
| Net unrealized (losses) on investments in debt securities AFS                                              |           |           |   |   |   |
| **Accumulated Other Comprehensive Income (Loss) [Line Items]**                                             |           |           |   |   |   |
| Other comprehensive income/(loss), pretax activity                                                         | (69,101)       |           | 16,795 | (236,880) | 83,175 |
| Other comprehensive income/(loss), tax effect                                                              | 16,984         |           | (5,910) | 38,938 | (29,892) |
| Other comprehensive income/(loss), net activity                                                            | (52,117)       |           | 10,885 | (197,942) | 53,283 |
| Total other comprehensive income/(loss), pretax activity                                                   | (66,751)       |           | 10,088 | (234,949) | 66,899 |
| Total other comprehensive income/(loss), tax effect                                                        | 16,406         |           | (3,550) | 38,621 | (24,043) |
| TOTAL OTHER COMPREHENSIVE (LOSS) / GAIN, NET OF TAX                                                        | (50,345)       |           | 6,538 | (196,328) | 42,856 |
| **AOCI Attributable to Parent, Net of Tax [Roll Forward]**                                                 |           |           |   |   |   |
| Equity, Beginning balance                                                                                  | (325,575)      | (140,498)      | (94,436) | (140,498) | (130,754) |
| Net Activity                                                                                               | (50,345)       |           | 6,538 | (196,328) | 42,856 |
| Cumulative effect of adoption of new ASUs                                                                  |           |           |   | (39,094) |   |
| Net Activity, upon adoption                                                                                |           |           |   | (235,422) |   |
| Equity, Ending balance                                                                                     | (375,920)      |           | (87,898) | (375,920) | (87,898) |
| Reclassification adjustment for net (gains)/losses included in net income/(expense) on non-OTTI securities |           |           |   |   |   |
| **Accumulated Other Comprehensive Income (Loss) [Line Items]**                                             |           |           |   |   |   |
| Reclassification adjustment, pretax activity                                                               | 2,350          |           | (6,707) | 1,931 | (16,276) |
| Reclassification adjustment, tax effect                                                                    | (578)          |           | 2,360 | (317) | 5,849 |
| Reclassification adjustment, net activity                                                                  | 1,772          |           | (4,347) | 1,614 | (10,427) |
| Pension and post-retirement actuarial gains/(losses)                                                       |           |           |   |   |   |
| **Accumulated Other Comprehensive Income (Loss) [Line Items]**                                             |           |           |   |   |   |
| Total other comprehensive income/(loss), pretax activity                                                   | 842            |           | 912 | 2,526 | 2,736 |
| Total other comprehensive income/(loss), tax effect                                                        | (216)          |           | (355) | (5,737) | (1,138) |
| TOTAL OTHER COMPREHENSIVE (LOSS) / GAIN, NET OF TAX                                                        | 626            |           | 557 | (3,211) | 1,598 |
| **AOCI Attributable to Parent, Net of Tax [Roll Forward]**                                                 |           |           |   |   |   |
| Equity, Beginning balance                                                                                  | (55,382)       | (51,545)       | (54,688) | (51,545) | (55,729) |
| Net Activity                                                                                               | 626            |           | 557 | (3,211) | 1,598 |
| Equity, Ending balance                                                                                     | (54,756)       |           | (54,131) | (54,756) | (54,131) |
| Accumulated other comprehensive (loss)/income                                                              |           |           |   |   |   |
| **AOCI Attributable to Parent, Net of Tax [Roll Forward]**                                                 |           |           |   |   |   |
| Equity, Beginning balance                                                                                  | (409,449)      | $ (198,431)    | (151,813) | (198,431) | (193,208) |
| Equity, Ending balance                                                                                     | $ (462,990)    |           | $ (145,210) | $ (462,990) | $ (145,210) |

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Amount before tax and reclassification adjustments of other comprehensive income (loss).
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Amount of tax expense (benefit) allocated to other comprehensive income (loss) before reclassification adjustment from accumulated other comprehensive income (loss).
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Amount after tax and reclassification adjustments of other comprehensive income (loss).
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Amount of tax expense (benefit) allocated to other comprehensive income (loss).
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Amount of stockholders' equity (deficit), net of receivables from officers, directors, owners, and affiliates of the entity, attributable to both the parent and noncontrolling interests. Amount excludes temporary equity. Alternate caption for the concept is permanent equity.
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