| **BORROWINGS (Narrative) (Details) - USD ($)**                                                                                                                                                                                                                                                                        |     | 12 Months Ended   |                  |                 |                 |               |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|-----|-------------------|------------------|-----------------|-----------------|---------------|
||
| **Debt Instrument [Line Items]**                                                                                                                                                                                                                                                                                      |     |              |             |            |            |          |   |
| Total borrowings and other debt obligations                                                                                                                                                                                                                                                                           | [1] |              | $ 49,086,103,000 |            |            |          | $ 39,679,382,000 |
| Borrowings repurchase                                                                                                                                                                                                                                                                                                 |     |              | $ 0              |            |            |          | $ 600,000 |
| Senior Notes | 2.00% senior notes, due January 2018                                                                                                                                                                                                                                                                   |     |              |             |            |            |          |   |
| **Debt Instrument [Line Items]**                                                                                                                                                                                                                                                                                      |     |              |             |            |            |          |   |
| Aggregate principal amount                                                                                                                                                                                                                                                                                            |     |              |             |            |            | $ 750,000,000 |   |
| Stated interest rate                                                                                                                                                                                                                                                                                                  |     |              |             |            |            | 2.00%         |   |
| Senior Notes | Senior Floating Rate Notes Due January 2018                                                                                                                                                                                                                                                            |     |              |             |            |            |          |   |
| **Debt Instrument [Line Items]**                                                                                                                                                                                                                                                                                      |     |              |             |            |            |          |   |
| Aggregate principal amount                                                                                                                                                                                                                                                                                            |     |              |             |            |            | $ 250,000,000 |   |
| Senior Notes | 2.65% senior notes, due April 2020                                                                                                                                                                                                                                                                     |     |              |             |            |            |          |   |
| **Debt Instrument [Line Items]**                                                                                                                                                                                                                                                                                      |     |              |             |            |            |          |   |
| Aggregate principal amount                                                                                                                                                                                                                                                                                            |     |              |             |            | $ 1,000,000,000 |          |   |
| Stated interest rate                                                                                                                                                                                                                                                                                                  |     |              |             |            | 2.65%           |          |   |
| Senior Notes | 4.50% senior notes, due July 2025                                                                                                                                                                                                                                                                      |     |              |             |            |            |          |   |
| **Debt Instrument [Line Items]**                                                                                                                                                                                                                                                                                      |     |              |             |            |            |          |   |
| Aggregate principal amount                                                                                                                                                                                                                                                                                            |     |              |             | $ 1,100,000,000 |            |          |   |
| Stated interest rate                                                                                                                                                                                                                                                                                                  |     |              |             | 4.50%           |            |          |   |
| Subsequent Event [Member] | Senior Notes Due August 2017                                                                                                                                                                                                                                                              |     |              |             |            |            |          |   |
| **Debt Instrument [Line Items]**                                                                                                                                                                                                                                                                                      |     |              |             |            |            |          |   |
| Basis spread on LIBOR                                                                                                                                                                                                                                                                                                 |     | 218.00%           |             |            |            |          |   |
| Subsequent Event [Member] | Senior Notes | Senior Notes Due August 2017                                                                                                                                                                                                                                               |     |              |             |            |            |          |   |
| **Debt Instrument [Line Items]**                                                                                                                                                                                                                                                                                      |     |              |             |            |            |          |   |
| Aggregate principal amount                                                                                                                                                                                                                                                                                            |     | $ 1,500,000,000.0 |             |            |            |          |   |
| Santander Bank | 2.00% senior notes, due January 2018                                                                                                                                                                                                                                                                 |     |              |             |            |            |          |   |
| **Debt Instrument [Line Items]**                                                                                                                                                                                                                                                                                      |     |              |             |            |            |          |   |
| Stated interest rate                                                                                                                                                                                                                                                                                                  |     |              | 2.00%            |            |            |          |   |
| Santander Bank | Senior Floating Rate Notes Due January 2018                                                                                                                                                                                                                                                          |     |              |             |            |            |          |   |
| **Debt Instrument [Line Items]**                                                                                                                                                                                                                                                                                      |     |              |             |            |            |          |   |
| Basis spread on LIBOR                                                                                                                                                                                                                                                                                                 |     |              | 93.00%           |            |            |          |   |
|                                                                                                                                                                                                                                                                                                                       |
| [1]The Company has interests in certain securitization trusts ("Trusts") that are considered variable interest entities ("VIEs") for accounting purposes. The Company consolidates VIEs where it is deemed the primary beneficiary. See Note 8 to these Consolidated Financial Statements for additional information. |

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|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Sum of the carrying values as of the balance sheet date of all debt, including all short-term borrowings, long-term debt, and capital lease obligations.
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| - Definition
Percentage points added to the reference rate to compute the variable rate on the debt instrument.
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|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Face (par) amount of debt instrument at time of issuance.
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
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| - Definition
Contractual interest rate for funds borrowed, under the debt agreement.
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| - 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.
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| - Definition
Fair value amount of debt instrument that was repurchased.
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