| **INVESTMENT SECURITIES (Gross Unrealized Loss and Fair Value of Securities Available for Sale) (Details) (USD $)In Thousands, unless otherwise specified** | Jun. 30, 2014 | Dec. 31, 2013 |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------|---------------|---------------|
| **Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]**                                                               |          |          |
| Less than 12 months, Fair Value                                                                                                                             | $ 1,007,943   | $ 6,182,194   |
| 12 months or longer, Fair Value                                                                                                                             | 5,249,334     | 1,023,099     |
| Total, Fair Value                                                                                                                                           | 6,257,277     | 7,205,293     |
| **Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]**                                                         |          |          |
| Less than 12 months, Unrealized Losses                                                                                                                      | (6,825)       | (307,072)     |
| 12 months or longer, Unrealized Losses                                                                                                                      | (212,176)     | (83,846)      |
| Total, Unrealized Losses                                                                                                                                    | (219,001)     | (390,918)     |
| Corporate debt securities [Member]                                                                                                                          |          |          |
| **Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]**                                                               |          |          |
| Less than 12 months, Fair Value                                                                                                                             | 67,225        | 743,041       |
| 12 months or longer, Fair Value                                                                                                                             | 216,573       | 32,020        |
| Total, Fair Value                                                                                                                                           | 283,798       | 775,061       |
| **Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]**                                                         |          |          |
| Less than 12 months, Unrealized Losses                                                                                                                      | (129)         | (10,868)      |
| 12 months or longer, Unrealized Losses                                                                                                                      | (2,711)       | (1,567)       |
| Total, Unrealized Losses                                                                                                                                    | (2,840)       | (12,435)      |
| Asset-backed securities [Member]                                                                                                                            |          |          |
| **Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]**                                                               |          |          |
| Less than 12 months, Fair Value                                                                                                                             | 576,287       | 803,685       |
| 12 months or longer, Fair Value                                                                                                                             | 95,495        | 24,316        |
| Total, Fair Value                                                                                                                                           | 671,782       | 828,001       |
| **Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]**                                                         |          |          |
| Less than 12 months, Unrealized Losses                                                                                                                      | (2,534)       | (4,111)       |
| 12 months or longer, Unrealized Losses                                                                                                                      | (618)         | (239)         |
| Total, Unrealized Losses                                                                                                                                    | (3,152)       | (4,350)       |
| Equity securities [Member]                                                                                                                                  |          |          |
| **Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]**                                                               |          |          |
| Less than 12 months, Fair Value                                                                                                                             | 30            | 5,020         |
| 12 months or longer, Fair Value                                                                                                                             | 9,854         | 4,797         |
| Total, Fair Value                                                                                                                                           | 9,884         | 9,817         |
| **Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]**                                                         |          |          |
| Less than 12 months, Unrealized Losses                                                                                                                      | 0             | (188)         |
| 12 months or longer, Unrealized Losses                                                                                                                      | (312)         | (302)         |
| Total, Unrealized Losses                                                                                                                                    | (312)         | (490)         |
| State and municipal securities [Member]                                                                                                                     |          |          |
| **Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]**                                                               |          |          |
| Less than 12 months, Fair Value                                                                                                                             | 103,244       | 710,456       |
| 12 months or longer, Fair Value                                                                                                                             | 514,405       | 126,345       |
| Total, Fair Value                                                                                                                                           | 617,649       | 836,801       |
| **Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]**                                                         |          |          |
| Less than 12 months, Unrealized Losses                                                                                                                      | (345)         | (45,972)      |
| 12 months or longer, Unrealized Losses                                                                                                                      | (12,904)      | (16,390)      |
| Total, Unrealized Losses                                                                                                                                    | (13,249)      | (62,362)      |
| Mortgage-backed securities, U.S. government agencies [Member]                                                                                               |          |          |
| **Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]**                                                               |          |          |
| Less than 12 months, Fair Value                                                                                                                             | 98,283        | 1,648,691     |
| 12 months or longer, Fair Value                                                                                                                             | 1,677,833     | 139,791       |
| Total, Fair Value                                                                                                                                           | 1,776,116     | 1,788,482     |
| **Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]**                                                         |          |          |
| Less than 12 months, Unrealized Losses                                                                                                                      | (205)         | (94,937)      |
| 12 months or longer, Unrealized Losses                                                                                                                      | (44,720)      | (8,952)       |
| Total, Unrealized Losses                                                                                                                                    | (44,925)      | (103,889)     |
| Mortgage-backed securities, FHLMC and FNMA debt securities [Member]                                                                                         |          |          |
| **Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]**                                                               |          |          |
| Less than 12 months, Fair Value                                                                                                                             | 162,874       | 2,271,301     |
| 12 months or longer, Fair Value                                                                                                                             | 2,735,174     | 695,830       |
| Total, Fair Value                                                                                                                                           | 2,898,048     | 2,967,131     |
| **Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]**                                                         |          |          |
| Less than 12 months, Unrealized Losses                                                                                                                      | (3,612)       | (150,996)     |
| 12 months or longer, Unrealized Losses                                                                                                                      | (150,911)     | (56,396)      |
| Total, Unrealized Losses                                                                                                                                    | $ (154,523)   | $ (207,392)   |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of accumulated pre-tax unrealized loss on securities classified as available-for-sale securities that have been in a loss position for twelve months or longer impacting Investments.
+ References
No definition available.
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of accumulated pre-tax unrealized loss on investments in available-for-sale securities thta have been in a loss position for less than twelve months impacting Investments.
+ References
No definition available.
+ Details**Name:**sov_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAggregatedLossesAccumulatedInInvestments**Namespace Prefix:**sov_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                       |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of accumulated pre-tax unrealized loss before deducting pre-tax unrealized gain on investments in available-for-sale securities impacting investments.
+ References
No definition available.
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| X                                                                                                                                                                                                                     |
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
This item represents the aggregate fair value of investments in debt and equity securities in an unrealized loss position which are categorized neither as held-to-maturity nor trading securities.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27290-111563
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
This item represents the aggregate fair value of investments in debt and equity securities categorized neither as held-to-maturity nor trading securities that have been in a continuous unrealized loss position for less than twelve months.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27337-111563Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27290-111563
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
This item represents the aggregate fair value of investments in debt and equity securities categorized neither as held-to-maturity nor trading securities that have been in a continuous unrealized loss position for twelve months or longer.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27337-111563Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27290-111563
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