| **BUSINESS SEGMENT INFORMATION (Tables)** | 3 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
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| **Segment Reporting [Abstract]**          |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |
| Schedule of Segment Reporting Information | The following tables present certain information regarding the Company’s segments.             For the Three-Month Period EndedSHUSA Reportable Segments    March 31, 2016Consumer and Business BankingCommercial BankingCommercial Real Estate Global Corporate BankingOther(2) SC(3)SC Purchase Price Adjustments(4)Eliminations(4) Total (in thousands)Net interest income$218,378$77,201$64,758$60,305$(21,401) $1,221,263$34,219$1,461 $1,656,184Total non-interest income187,26512,6022,06217,26734,279 345,61513,782(11,237) 601,635Provision/(release)  for credit losses49661,66112,68047,795(9,706) 706,574100,939— 920,439Total expenses408,46544,59519,59934,952145,746 543,48214,733(12,937) 1,198,635Income/(loss) before income taxes(3,318)(16,453)34,541(5,175)(123,162) 316,822(67,671)3,161 138,745            Intersegment (expense)/revenue(1)548990500(2,109)71 ——— —Total assets21,293,16111,734,67015,552,07212,555,44532,137,759 37,825,803—— 131,098,910            (1)Intersegment revenue/(expense) represents charges or credits for funds used or provided by each of the segments and is included in net interest income.(2)Other is not considered a segment and includes earnings from non-strategic assets, the investment portfolio, interest expense on the Bank’s and Parent Company's borrowings and other debt obligations, amortization of intangible assets and certain unallocated corporate income and indirect expenses.(3)Management of SHUSA manages SC by analyzing the pre-Change in Control results of SC as disclosed in this column.(4)Purchase Price Adjustments represents the impact that SC purchase marks had on the results of SC included within the consolidated operations of SHUSA, while eliminations eliminate intercompany transactions.NOTE 17. BUSINESS SEGMENT INFORMATION (continued)            For the Three-Month Period EndedSHUSA Reportable Segments    March 31, 2015Consumer and Business BankingCommercial BankingCommercial Real Estate Global Corporate BankingOther(2) SC(3)SC Purchase Price Adjustments(4)Eliminations(4) Total (in thousands)Net interest income$204,714$64,238$65,320$49,090$15,937 $1,160,005$94,768$87 $1,654,159Total non-interest income155,26811,6587,83515,97123,472 321,64059,202(15,723) 579,323Provision/(release) for credit losses6971,61410,8382,75131,101 674,688322,524— 1,044,213Total expenses420,39144,59317,67324,97443,599 444,98813,743(13,676) 996,285Income/(loss) before income taxes(61,106)29,68944,64437,336(35,291) 361,969(182,297)(1,960) 192,984            Intersegment revenue/(expense)(1)363976359(2,325)627 ——— —Total assets22,394,92515,497,92514,037,58011,763,67225,093,043 34,638,558—— 123,425,703            (1)Intersegment revenue/(expense) represents charges or credits for funds used or provided by each of the segments and is included in net interest income.(2)Other is not considered a segment and includes earnings from non-strategic assets, the investment portfolio, interest expense on the Bank’s and Parent Company's borrowings and other debt obligations, amortization of intangible assets and certain unallocated corporate income and indirect expenses.(3)Management of SHUSA manages SC by analyzing the pre-Change in Control results of SC as disclosed in this column.(4)Purchase Price Adjustments represent the impact that SC purchase marks had on the results of SC included within the consolidated operations of SHUSA, while eliminations eliminate intercompany transactions. |

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| - Definition
Tabular disclosure of the profit or loss and total assets for each reportable segment. An entity discloses certain information on each reportable segment if the amounts (a) are included in the measure of segment profit or loss reviewed by the chief operating decision maker or (b) are otherwise regularly provided to the chief operating decision maker, even if not included in that measure of segment profit or loss.
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