| **Related Party Transactions**            | 9 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
|-------------------------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
||
| **Related Party Transactions [Abstract]** |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
| Related Party Transactions                | RELATED PARTY TRANSACTIONSThe parties related to the Company are deemed to include, in addition to its subsidiaries, jointly controlled entities, the Bank’s key management personnel (the members of its Board of Directors and certain officers at the level of executive vice president or above, together with their close family members) and the entities over which the key management personnel may exercise significant influence or control. Each of the agreements was made in the ordinary course of business and on market terms.The Company has various debt agreements with Banco Santander. For a listing of these debt agreements, see the Company's Annual Report on Form 10-K for the year ended December 31, 2012.The Company has $2.5 billion of public securities consisting of various senior note obligations, trust preferred securities obligations and preferred stock issuances. Banco Santander owned approximately 24.1% of these securities as of September 30, 2013.The Company has entered into derivative agreements with Banco Santander and Abbey National Treasury Services PLC which consist primarily of customer related derivatives, and swap agreements to hedge interest rate risk and foreign currency exposure. These contracts had notional values of $3.1 billion and $3.5 billion, respectively, as of September 30, 2013 and $3.5 billion and $1.0 billion, respectively, as of December 31, 2012.In 2006, Banco Santander provided confirmation of standby letters of credit issued by the Bank. During the nine-month periods ended September 30, 2013 and 2012, the average unfunded balance outstanding under these commitments was $35.0 million and $311.3 million, respectively. The Bank paid approximately $0.1 million and $0.2 million in fees to Banco Santander in the three-month and nine-month periods endedSeptember 30, 2013, respectively, in connection with these commitments, compared to $0.3 million and $2.4 million in fees in the corresponding periods in the prior year. SHUSA has a $500 million line of credit with Banco Santander that began in November 2012. There was no activity during the nine-month period endedSeptember 30, 2013 or the corresponding period in 2012 related to this line of credit.In addition, during the three-month and nine-month periods endedSeptember 30, 2013, respectively, the Company paid $0.5 million in rental payments to Banco Santander compared to $0.7 million in the corresponding periods in 2012.In the ordinary course of business, we may provide loans to our executive officers, directors, and principal stockholders, also known as Regulation O insiders. Pursuant to our policy, such loans are issued on the same terms as those prevailing at the time for comparable loans to unrelated persons and do not involve more than the normal risk of collectability. The outstanding balance of these loans was $8.6 million and $6.5 million at September 30, 2013 and December 31, 2012, respectively.NOTE 13.  RELATED PARTY TRANSACTIONS (continued) The Company and its affiliates have entered into various service agreements with Banco Santander and its affiliates.  Those agreements include the following:•NW Services Co., a Banco Santander affiliate doing business as Aquanima, is under contract with the Bank to provide procurement services, with fees paid in the three-month and nine-month periods endedSeptember 30, 2013 in the amount of $0.8 million and $2.5 million, respectively, compared to $0.9 million and $2.8 million for the corresponding periods in 2012. There were no payables in connection with this agreement at September 30, 2013 or December 31, 2012, respectively. The fees related to this agreement are recorded in Outside services in the Condensed Consolidated Statement of Operations. •Geoban, S.A., a Banco Santander affiliate, is under contract with the Bank to provide services in connection with debit card disputes and claims support, and consumer and mortgage loan set-up and review, with fees paid in the three-month and nine-month periods endedSeptember 30, 2013 in the amount of $3.9 million and $13.2 million, respectively, compared to $1.9 million and $15.0 million for the corresponding periods in 2012. In addition, the Company had payables with Geoban, S.A. in the amount of $2.3 million at December 31, 2012. There were no payables in connection with this agreement at September 30, 2013.The fees related to this agreement are recorded in Outside services in the Condensed Consolidated Statement of Operations. •Ingenieria de Software Bancario S.L., a Banco Santander affiliate, is under contract with the Bank to provide information technology development, support and administration, with fees paid in the three-month and nine-month periods endedSeptember 30, 2013 in the amount of $15.2 million and $87.9 million, respectively, compared to $27.6 million and $97.9 million for the corresponding periods in 2012. In addition, as of September 30, 2013 and December 31, 2012, the Company had payables with Ingenieria De Software Bancario S.L. in the amounts of $13.3 million and $27.9 million, respectively. The fees related to this agreement are capitalized in Premises and equipment on the Condensed Consolidated Balance Sheet.•Produban Servicios Informaticos Generales S.L., a Banco Santander affiliate, is under contract with the Bank to provide professional services, and administration and support of information technology production systems, telecommunications and internal/external applications, with fees paid in the three-month and nine-month periods endedSeptember 30, 2013 in the amount of $21.9 million and $64.4 million, respectively, compared to $25.0 million and $76.3 million for the corresponding periods in 2012. In addition, as of September 30, 2013 and December 31, 2012, the Company had payables with Produban Servicios Informaticos Generales S.L. in the amounts of $4.9 million and $5.3 million, respectively. The fees related to this agreement are recorded in Occupancy and equipment expenses and Technology expense in the Condensed Consolidated Statement of Operations. •Santander Back-Offices Globales Mayoristas S.A., a Banco Santander affiliate, is under contract with the Bank to provide logistical support for the Bank’s derivative and hedging transactions and programs. In the three-month and nine-month periods endedSeptember 30, 2013 and 2012, fees in the amounts of $0.1 million and $0.3 million, respectively, were paid to Santander Back-Offices Globales Mayoristas S.A. with respect to this agreement. There were no payables in connection with this agreement at September 30, 2013 or December 31, 2012. The fees related to this agreement are recorded in Outside services in the Condensed Consolidated Statement of Operations. •Santander Global Facilities (“SGF”), a Banco Santander affiliate, is under contract with the Bank to provide (i) administration and management of employee benefits and payroll functions for the Bank and other affiliates, including employee benefits and payroll processing services provided by third party vendors sponsored by SGF, and (ii) property management and related services. In the three-month and nine-month periods endedSeptember 30, 2013, fees in the amounts of $3.0 million and $8.6 million were paid to SGF with respect to this agreement, compared to $2.3 million and $7.1 million for the corresponding periods in 2012. There were no payables in connection with this agreement at September 30, 2013 or December 31, 2012. The fees related to this agreement are recorded in Outside services in the Condensed Consolidated Statement of Operations. NOTE 13.  RELATED PARTY TRANSACTIONS (continued) •Santander Securities LLC, a Banco Santander affiliate, is under contract with the Bank to provide integrated services and conduct broker-dealer activities and insurance services. Santander Securities collects amounts due from customers on behalf of the Bank and remits those amounts net of fees. As of September 30, 2013, the Company had receivables with Santander Securities in the amount of $3.8 million, compared to $3.9 million as of December 31, 2012 which are recorded within Other assets on the Condensed Consolidated Balance Sheet. Fees recognized related to this agreement were $13.5 million and $37.7 million for the three-month and nine-month periods ended September 30, 2013, respectively, and $0.8 million for the corresponding periods in 2012 which are recognized within Consumer fees in the Condensed Consolidated Statement of Operations.  There were no payables in connection with this agreement at September 30, 2013 or December 31, 2012. •During the three-month and nine-month periods endedSeptember 30, 2013, the Company recorded expenses of $4.2 million and $13.6 million, respectively, related to transactions with SCUSA, compared to $6.0 million and $20.7 million for the corresponding periods in 2012, which are recorded within Loan expense on the Condensed Consolidated Statement of Operations. In addition, as of September 30, 2013 and December 31, 2012, the Company had receivables and prepaid expenses with SCUSA in the amounts of $40.0 million and $59.2 million, respectively, which are recorded within Other Assets on the Condensed Consolidated Balance Sheet and payables to SCUSA in the amounts of $3.8 million and $4.5 million which are recorded within Accrued Expenses and Payables on the Condensed Consolidated Balance Sheet. The activity is primarily related to SCUSA's servicing of certain outstanding Bank loan portfolios and dividends paid by SCUSA to SHUSA. On June 28, 2013, the Bank entered into a servicing and sourcing agreement with SCUSA for Chrysler dealer lending opportunities, under which SCUSA will provide servicing on loans originated by the Bank. On August 16, 2013, the Company purchased performing dealer loans with an outstanding balance of $204.8 million from SCUSA, which have been classified as commercial and industrial loans. |

| X                                                                                                                                                                    |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_RelatedPartyTransactionsAbstract**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The entire disclosure for related party transactions. Examples of related party transactions include transactions between (a) a parent company and its subsidiary; (b) subsidiaries of a common parent; (c) and entity and its principal owners; and (d) affiliates.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 850 -SubTopic 10 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39622-107864Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 850 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39603-107864Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 850 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Paragraph b -Article 3AReference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08.(k)) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 08 -Paragraph k -Article 4Reference 7: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 850 -SubTopic 10 -Section 50 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39691-107864Reference 8: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 850 -SubTopic 10 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39678-107864
+ Details**Name:**us-gaap_RelatedPartyTransactionsDisclosureTextBlock**Namespace Prefix:**us-gaap_**Data Type:**nonnum:textBlockItemType**Balance Type:**na**Period Type:**duration |