| **BORROWINGS (Tables)**                          | 3 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
|--------------------------------------------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
||
| SHUSA                                            |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
| **Debt Instrument [Line Items]**                 |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
| Schedule of Borrowings and Other Debt Obligation | The following table presents information regarding the Parent Company borrowings and other debt obligations at the dates indicated: March 31, 2016 December 31, 2015 Balance EffectiveRate Balance EffectiveRate (dollars in thousands)4.625% senior notes, due April 2016 $475,982 4.85% $475,723 4.85%Senior notes with related party, due August 2017(1)1,500,000 2.80% — —%3.45% senior notes, due August 2018497,999 3.62% 497,800 3.62%2.65% senior notes, due April 2020993,527 2.82% 993,151 2.82%4.50% senior notes, due July 20251,094,599 4.56% 1,094,483 4.56%Junior subordinated debentures - Capital Trust VI, due June 203669,781 7.91% 69,775 7.91%Common securities - Capital Trust VI10,000 7.91% 10,000 7.91%Junior subordinated debentures - Capital Trust IX, due July 2036149,411 2.43% 149,404 2.18%Common securities - Capital Trust IX4,640 2.43% 4,640 2.18%     Total Parent Company borrowings and other debt obligations$4,795,939 3.57% $3,294,976 3.91%(1)  These notes will bear interest at a rate equal to three-month LIBOR plus 218 basis points per annum.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |
| Santander Bank                                   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
| **Debt Instrument [Line Items]**                 |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
| Schedule of Borrowings and Other Debt Obligation | The following table presents information regarding the Bank's borrowings and other debt obligations at the dates indicated:  March 31, 2016 December 31, 2015 Balance EffectiveRate Balance EffectiveRate (dollars in thousands)2.00% senior notes, due January 2018$746,818 2.24% $746,381 2.24%Senior notes, due January 2018(1)249,486 1.72% 249,415 1.31%Overnight federal funds purchased100,000 0.35% — —%8.750% subordinated debentures, due May 2018498,346 8.92% 498,175 8.92%Subordinated term loan, due February 2019124,979 6.53% 130,899 6.15%FHLB advances, maturing through July 201912,835,000 1.24% 13,885,000 1.40%REIT preferred, due May 2020155,310 13.48% 154,930 13.66%Subordinated term loan, due August 202230,445 8.28% 30,344 7.89%     Total Bank borrowings and other debt obligations$14,740,384 1.74% $15,695,144 1.85%(1)  These notes will bear interest at a rate equal to three-month LIBOR plus 93 basis points per annum.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |
| SC                                               |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
| **Debt Instrument [Line Items]**                 |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
| Schedule of Borrowings and Other Debt Obligation | The following tables present information regarding SC's credit facilities as of March 31, 2016 and December 31, 2015: March 31, 2016 Balance EffectiveRate Assets Pledged Restricted Cash Pledged (dollars in thousands)Warehouse line, maturing on various dates(1)$898,785 1.65% $1,268,593 $33,876Warehouse line, due June 2016328,484 1.53% 470,935 —Warehouse line, due November 2016(2)175,000 1.99% — —Warehouse line, due November 2016(2)250,000 1.99% — 2,502Warehouse line, due July 2017(3)1,136,620 1.26% 1,327,405 39,890Warehouse line, due July 2017(4)2,151,543 1.37% 3,301,792 59,169Warehouse line, due December 20171,342,277 1.59% 1,903,553 45,797Warehouse line, due January 201873,000 3.13% 102,309 —Warehouse line, due March 2018(5)886,199 1.26% 1,287,618 28,733Repurchase facility, due December 2016(6)1,147,361 2.51% — 44,767Line of credit with related party, due December 2016(7)500,000 2.74% — —Line of credit with related party, due December 2016(7)1,000,000 2.70% — —Line of credit with related party, due December 2018(7)975,000 2.94% — —     Total SC revolving credit facilities$10,864,269 1.89% $9,662,205 $254,734(1)  As of March 31, 2016, half of the outstanding balance on this facility matures in March 2017 and half matures in March 2018. (2)  These lines are collateralized by residuals retained by SC.(3)  This line is held exclusively for financing Chrysler Capital Loans.(4)  This line is held exclusively for financing Chrysler Capital Leases.(5)  As of December 31, 2015 this warehouse line was due at September 2017.(6)  This repurchase facility is collateralized by securitization notes payable retained by SC. No portion of this facility is unsecured. This facility has rolling 30-day and 90-day maturities.(7)  These lines are also collateralized by securitization notes payable and residuals retained by SC. As of March 31, 2016, $1.6 billion of the aggregate outstanding balances on these credit facilities was unsecured. NOTE 10. BORROWINGS (continued) December 31, 2015 Balance EffectiveRate Assets Pledged Restricted Cash Pledged (dollars in thousands)Warehouse line, maturing on various dates(1)$808,135 1.29% $1,137,257 $24,942Warehouse line, due June 2016378,301 1.48% 535,737 —Warehouse line, due November 2016(2)175,000 1.90% — —Warehouse line, due November 2016(2)250,000 1.90% — 2,501Warehouse line, due July 2017(3)682,720 1.35% 809,185 20,852Warehouse line, due July 2017(4)2,247,443 1.41% 3,412,321 48,589Warehouse line, due September 2017565,399 1.20% 824,327 15,759Warehouse line, due December 2017 (5)944,877 1.56% 1,345,051 32,038Repurchase facility, due December 2016(6)850,904 2.07% — 34,166Line of credit with related party, due December 2016(7)500,000 2.65% — —Line of credit with related party, due December 2016(7)1,000,000 2.61% — —Line of credit with related party, due December 2018(7)800,000 2.84% — —     Total SC revolving credit facilities$9,202,779 1.81% $8,063,878 $178,847(1)  As of December 31, 2015, half of the outstanding balance on this facility matured in March 2016 and half matured in March 2017. On March 29, 2016, the facility was amended to, among other changes, extend the maturity for half of the balance to March 2017 and half to March 2018.(2)  These lines are collateralized by residuals retained by SC.(3)  This line is held exclusively for financing Chrysler Capital Loans.(4)  This line is held exclusively for financing Chrysler Capital Leases.(5)  In December 2015, the commitment on this warehouse line was amended to extend the commitment termination date to December 2017.(6)  This repurchase facility is collateralized by securitization notes payable retained by SC. No portion of this facility is unsecured. This facility has rolling 30-day and 90-day maturities.(7)  These lines are also collateralized by securitization notes payable and residuals retained by SC. As of December 31, 2015, $1.4 billion of the aggregate outstanding balances on these credit facilities was unsecured.The following tables present information regarding SC's secured structured financings as of March 31, 2016 and December 31, 2015: March 31, 2016 Balance Initial Note Amounts Issued Initial Weighted Average Interest Rate Range Collateral Restricted Cash (dollars in thousands)SC public securitizations, maturing on various dates(1)$12,565,678 $26,563,082 0.89% - 2.44% $16,452,180 $1,396,275SC privately issued amortizing notes, maturing on various dates(1)7,790,231 11,535,991 0.88% - 2.81% 11,029,245 498,836     Total SC secured structured financings$20,355,909 $38,099,073 0.88% - 2.81% $27,481,425 $1,895,111(1)  SC has entered into various securitization transactions involving its retail automotive installment loans and leases. These transactions are accounted for as secured financings and therefore both the securitized RICs, and the related securitization debt issued by SPEs, remain on the Condensed Consolidated Balance Sheets. The maturity of this debt is based on the timing of repayments from the securitized assets.NOTE 10. BORROWINGS (continued) December 31, 2015 Balance Initial Note Amounts Issued Initial Weighted Average Interest Rate Range Collateral Restricted Cash (dollars in thousands)SC public securitizations, maturing on various dates(1)$12,679,987 $24,923,292 0.89% - 2.29% $16,256,067 $1,242,857SC privately issued amortizing notes, maturing on various dates(1)8,213,217 11,729,171 0.88% - 2.81% 11,495,352 457,840     Total SC secured structured financings$20,893,204 $36,652,463 0.88% - 2.81% $27,751,419 $1,700,697(1)  SC has entered into various securitization transactions involving its retail automotive installment loans and leases. These transactions are accounted for as secured financings and therefore both the securitized RICs, and the related securitization debt issued by SPEs, remain on the Condensed Consolidated Balance Sheets. The maturity of this debt is based on the timing of repayments from the securitized assets. |

| X                                                                                                                                                                                                                                                                                                                                                                                                               |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - 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.
+ References
No definition available.
+ Details**Name:**us-gaap_DebtInstrumentLineItems**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Tabular disclosure of information pertaining to short-term and long-debt instruments or arrangements, including but not limited to identification of terms, features, collateral requirements and other information necessary to a fair presentation.
+ References
No definition available.
+ Details**Name:**us-gaap_ScheduleOfDebtTableTextBlock**Namespace Prefix:**us-gaap_**Data Type:**nonnum:textBlockItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                       |
|-----------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**dei_LegalEntityAxis=us-gaap_ParentCompanyMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                      |
|----------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**dei_LegalEntityAxis=us-gaap_SubsidiariesMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                        |
|--------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**dei_LegalEntityAxis=sov_SCMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |