| **INVESTMENT SECURITIES (Details) (USD $)In Thousands, unless otherwise specified** | Jun. 30, 2014 | Dec. 31, 2013 |
|-------------------------------------------------------------------------------------|---------------|---------------|
| **Schedule of Available-for-sale Securities [Line Items]**                          |          |          |
| Amortized Cost                                                                      | $ 11,786,164  | $ 11,970,063  |
| Gross Unrealized Gains                                                              | 107,879       | 67,095        |
| Gross Unrealized Loss                                                               | (219,001)     | (390,918)     |
| Fair Value                                                                          | 11,675,042    | 11,646,240    |
| US Treasury and government agency securities [Member]                               |          |          |
| **Schedule of Available-for-sale Securities [Line Items]**                          |          |          |
| Amortized Cost                                                                      | 8,000         | 24,993        |
| Gross Unrealized Gains                                                              | 0             | 4             |
| Gross Unrealized Loss                                                               | 0             | 0             |
| Fair Value                                                                          | 8,000         | 24,997        |
| Corporate debt securities [Member]                                                  |          |          |
| **Schedule of Available-for-sale Securities [Line Items]**                          |          |          |
| Amortized Cost                                                                      | 2,191,038     | 2,195,004     |
| Gross Unrealized Gains                                                              | 46,151        | 35,611        |
| Gross Unrealized Loss                                                               | (2,840)       | (12,435)      |
| Fair Value                                                                          | 2,234,349     | 2,218,180     |
| Asset-backed securities [Member]                                                    |          |          |
| **Schedule of Available-for-sale Securities [Line Items]**                          |          |          |
| Amortized Cost                                                                      | 2,584,562     | 2,727,235     |
| Gross Unrealized Gains                                                              | 23,251        | 9,345         |
| Gross Unrealized Loss                                                               | (3,152)       | (4,350)       |
| Fair Value                                                                          | 2,604,661     | 2,732,230     |
| Equity securities [Member]                                                          |          |          |
| **Schedule of Available-for-sale Securities [Line Items]**                          |          |          |
| Amortized Cost                                                                      | 10,473        | 10,331        |
| Gross Unrealized Gains                                                              | 2             | 0             |
| Gross Unrealized Loss                                                               | (312)         | (490)         |
| Fair Value                                                                          | 10,163        | 9,841         |
| State and municipal securities [Member]                                             |          |          |
| **Schedule of Available-for-sale Securities [Line Items]**                          |          |          |
| Amortized Cost                                                                      | 1,807,170     | 1,891,996     |
| Gross Unrealized Gains                                                              | 36,355        | 20,515        |
| Gross Unrealized Loss                                                               | (13,249)      | (62,362)      |
| Fair Value                                                                          | 1,830,276     | 1,850,149     |
| Mortgage-backed securities, U.S. government agencies [Member]                       |          |          |
| **Schedule of Available-for-sale Securities [Line Items]**                          |          |          |
| Amortized Cost                                                                      | 1,910,373     | 1,904,178     |
| Gross Unrealized Gains                                                              | 511           | 134           |
| Gross Unrealized Loss                                                               | (44,925)      | (103,889)     |
| Fair Value                                                                          | 1,865,959     | 1,800,423     |
| Mortgage-backed securities, FHLMC and FNMA debt securities [Member]                 |          |          |
| **Schedule of Available-for-sale Securities [Line Items]**                          |          |          |
| Amortized Cost                                                                      | 3,260,969     | 3,202,428     |
| Gross Unrealized Gains                                                              | 1,356         | 1,486         |
| Gross Unrealized Loss                                                               | (154,523)     | (207,392)     |
| Fair Value                                                                          | 3,107,802     | 2,996,522     |
| Mortgage-backed securities, Non-agency securities [Member]                          |          |          |
| **Schedule of Available-for-sale Securities [Line Items]**                          |          |          |
| Amortized Cost                                                                      | 13,579        | 13,898        |
| Gross Unrealized Gains                                                              | 253           | 0             |
| Gross Unrealized Loss                                                               | 0             | 0             |
| Fair Value                                                                          | $ 13,832      | $ 13,898      |

| X                                                                                                                                                                                                                                                                                                                                                                                                                         |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of accumulated pre-tax unrealized gains before deducting pre-tax unrealized losses on investments in available-for-sale securities impacting investments.
+ References
No definition available.
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| 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.
+ Details**Name:**sov_AvailableForSaleSecuritiesGrossUnrealizedLossAccumulatedInInvestments**Namespace Prefix:**sov_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 25 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=28360136&loc=d3e22054-111558Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (aa) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26610-111562
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.2) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682
+ Details**Name:**us-gaap_AvailableForSaleSecuritiesAmortizedCost**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                 |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
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