| **PARENT COMPANY FINANCIAL INFORMATION (As Restated) (Tables)**                  | 12 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |
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| **Condensed Financial Information of Parent Company Only Disclosure [Abstract]** |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
| BALANCE SHEETS                                                                   | BALANCE SHEETS  AT DECEMBER 31,  2015 2014 (1)  (in thousands)Assets    Cash and cash equivalents $3,169,366 $2,099,992Loans to non-bank subsidiaries 300,000 300,000Investment in subsidiaries:    Bank subsidiary 9,091,027 8,975,964Non-bank subsidiaries 7,793,321 10,107,436Premises and equipment, net(3) 57,622 122Equity method investments 22,981 29,181Restricted cash 73,060 82,019Other assets(2) 254,839 272,305Total assets $20,762,216 $21,867,019Liabilities and stockholder's equity    Borrowings and other debt obligations(2) $3,294,976 $1,804,297Borrowings from non-bank subsidiaries 140,144 139,184Deferred tax liabilities, net 57,620 1,155,336Other liabilities 132,671 93,141Total liabilities 3,625,411 3,191,958Stockholder's equity 17,136,805 18,675,061Total liabilities and stockholder's equity $20,762,216 $21,867,019(1) Reflects the impact of the Change in Control and 11 months of activity of SC as a consolidated subsidiary.(2)Balances as of December 31, 2014 include re-classification of debt issuance costs from Other assets to Borrowings and other debt obligations in accordance with the adoption of ASU 2015-03. Refer to Note 1 to the Consolidated Financial Statements for additional details related to this ASU implementation.(3)  During 2015, the Company added a significant amount of premises and equipment, primarily computer hardware and software, which was assigned to the Parent Company. In prior years, premises and equipment was included within the Other assets line of the Parent Company Balance Sheet.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |
| STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME                                | STATEMENTS OF OPERATIONS AND COMPREHENSIVE (LOSS)/INCOME  YEAR ENDED DECEMBER 31,  2015 2014 (1) 2013 (2)  (in thousands)Dividends from non-bank subsidiaries $— $31,649 $—Interest income 7,439 4,987 3,365Income from equity method investments 262 24,804 460,691Gain on Change in Control — 2,417,563 —Other income 2,688 2,049 2,009Total income 10,389 2,481,052 466,065Interest expense 108,811 70,816 161,812Other expense 287,650 142,681 51,773Total expense 396,461 213,497 213,585(Loss)/income before income taxes and equity in earnings of subsidiaries (386,072) 2,267,555 252,480Income tax (benefit)/provision (1,062,338) 884,110 (1,650)Income before equity in earnings of subsidiaries 676,266 1,383,445 254,130Equity in undistributed earnings / (deficits) of:      Bank subsidiary 148,335 327,676 312,627Non-bank subsidiaries (2,304,983) 723,691 89,103Net (loss)/income (1,480,382) 2,434,812 655,860Other comprehensive (loss)/income, net of tax:      Net unrealized (losses)/gains on cash flow hedge derivative financial instruments (2,322) 25,163 39,751Net unrealized (losses)/gains recognized on investment securities (43,511) 146,877 (359,616)Amortization of defined benefit plans 2,602 (14,082) 11,163Total other comprehensive (loss)/income (43,231) 157,958 (308,702)Comprehensive (loss)/income $(1,523,613) $2,592,770 $347,158(1) Reflects the impact of the Change in Control and 11 months of activity of SC as a consolidated subsidiary.(2) Balances as of December 31, 2013 presented with SC being accounted for as an equity method investment at that date.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |
| STATEMENT OF CASH FLOWS                                                          | STATEMENT OF CASH FLOWS  FOR THE YEAR ENDED DECEMBER 31  2015 2014 (1) 2013 (2)  (in thousands)CASH FLOWS FROM OPERATING ACTIVITIES:      Net (loss)/income $(1,480,382) $2,434,812 $655,860Adjustments to reconcile net income to net cash (paid in)/provided by operating activities:      Gain on SC Change in Control — (2,280,027) —Net gain on sale of SC shares — (137,536) —Deferred tax (expense) / benefit (1,085,642) 1,033,824 85,408Undistributed (earnings) / deficit of:      Bank subsidiary (148,335) (327,676) (312,627)Non-bank subsidiaries 2,304,983 (723,691) (89,103)Stock based compensation expense 25 449 2,057Remittance to Santander for stock based compensation — (1,656) (3,877)Equity earnings from equity method investments (262) (24,804) (460,691)Dividends from equity method investments — — 188,661Net change in other assets and other liabilities 42,935 (17,052) (284,839)Net cash (paid in) / provided by operating activities (366,678) (43,357) (219,151)CASH FLOWS FROM INVESTING ACTIVITIES:      Net capital (contributed to)/returned from subsidiaries (827) 146,886 178,266Net change in restricted cash 8,959 (82,019) —Net (increase)/decrease in loans to subsidiaries — (300,000) —Proceeds from sale of SC shares — 320,145 —Proceeds from the sales of equity method investments 14,947 — —Purchases of premises and equipment (58,524) — —Net cash (used in) / provided by investing activities (35,445) 85,012 178,266CASH FLOWS FROM FINANCIAL ACTIVITIES:      Repayment of other debt obligations (600,000) — (481,267)Net proceeds received from senior notes and senior credit facility 2,085,205 — 500,000Net change in borrowings 960 6,906 (1,038)Dividends to preferred stockholders (14,600) (14,600) (14,600)Net proceeds from the issuance of common stock — 1,771,000 —Impact of SC stock option activity (68) — —Net cash provided by/(used in) financing activities 1,471,497 1,763,306 3,095Increase/(Decrease) in cash and cash equivalents 1,069,374 1,804,961 (37,790)Cash and cash equivalents at beginning of period 2,099,992 295,031 332,821Cash and cash equivalents at end of period $3,169,366 $2,099,992 $295,031(1) Reflects the impact of the Change in Control and 11 months of activity of SC as a consolidated subsidiary.(2) Balances as of December 31, 2013 presented with SC being accounted for as an equity method investment at that date. |

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| - Definition
Tabular disclosure of components of comprehensive income (loss). Includes, but is not limited to, foreign currency translation adjustments, foreign currency transactions  designated as economic hedges of a net investment in foreign entity, gain (loss) and prior service cost (credit) for pension plans and other postretirement benefit plans.
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Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=36458714&loc=d3e526-108580
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Tabular disclosure of condensed balance sheet, including, but not limited to, balance sheets of consolidated entities and consolidation eliminations.
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Tabular disclosure of condensed cash flow statement, including, but not limited to, cash flow statements of consolidated entities and consolidation eliminations.
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