LOANS AND ALLOWANCE FOR CREDIT LOSSES (Portfolio Segments and Classes) (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014		Dec. 31, 2013
Loans Receivable [Line Items]
Loans held for investment	$ 75,637,888	[1],[2]	$ 49,921,677	[1],[2]
Corporate banking [Member]
Loans Receivable [Line Items]
Financing receivable	3,412,053		3,767,870
Middle market commercial real estate [Member]
Loans Receivable [Line Items]
Financing receivable	3,611,134		3,510,372
Santander real estate capital [Member]
Loans Receivable [Line Items]
Financing receivable	1,885,808		2,025,644
Residential mortgages [Member]
Loans Receivable [Line Items]
Financing receivable	9,651,706		9,672,204
Home equity loans and lines of credit [Member]
Loans Receivable [Line Items]
Financing receivable	6,190,475		6,311,694
Loans held for investment	6,190,475	[3]	6,311,694
Consumer loans not secured by real estate [Member] | Retail installment contracts and auto loans [Member]
Loans Receivable [Line Items]
Loans held for investment	21,623,534	[4]	81,804	[4]
Consumer loans not secured by real estate [Member] | Personal unsecured loan [Member]
Loans Receivable [Line Items]
Loans held for investment	1,861,805		493,785
Consumer loans not secured by real estate [Member] | Other consumer [Member]
Loans Receivable [Line Items]
Loans held for investment	1,457,058	[5]	1,321,985	[5]
Commercial Loans Held for Investment [Member]
Loans Receivable [Line Items]
Financing receivable	35,001,993		32,151,222
Commercial Loans Held for Investment [Member] | Commercial real estate loans [Member]
Loans Receivable [Line Items]
Financing receivable	8,897,785		9,303,885
Commercial Loans Held for Investment [Member] | Commercial and industrial loans [Member]
Loans Receivable [Line Items]
Financing receivable	14,954,380	[6]	12,820,417	[6]
Loans held for sale	41,100		17,900
Commercial Loans Held for Investment [Member] | Multi-family loans [Member]
Loans Receivable [Line Items]
Financing receivable	9,229,611		8,237,029
Commercial Loans Held for Investment [Member] | Other commercial [Member]
Loans Receivable [Line Items]
Financing receivable	1,920,217		1,789,891
Commercial Loans Held for Investment [Member] | Corporate banking [Member] | Commercial real estate loans [Member]
Loans Receivable [Line Items]
Financing receivable	3,412,053		3,767,869
Commercial Loans Held for Investment [Member] | Middle market commercial real estate [Member]
Loans Receivable [Line Items]
Loans held for sale	11,200		0
Commercial Loans Held for Investment [Member] | Middle market commercial real estate [Member] | Commercial real estate loans [Member]
Loans Receivable [Line Items]
Financing receivable	3,599,924	[7]	3,510,371	[7]
Commercial Loans Held for Investment [Member] | Santander real estate capital [Member] | Commercial real estate loans [Member]
Loans Receivable [Line Items]
Financing receivable	1,885,808		2,025,645
Loans Held-for-investment [Member]
Loans Receivable [Line Items]
Financing receivable	40,635,895		17,770,455
Loans Held-for-investment [Member] | Consumer loans secured by real estate [Member]
Loans Receivable [Line Items]
Financing receivable	15,693,498		15,872,881
Loans Held-for-investment [Member] | Retail installment contracts and auto loans [Member]
Loans Receivable [Line Items]
Loans held for sale	89,400		0
Loans Held-for-investment [Member] | Residential mortgages [Member]
Loans Receivable [Line Items]
Loans held for sale	$ 148,700		$ 111,000

[1] Loans held for investment includes $1.3 billion and $0.0 billion of loans recorded at fair value at June 30, 2014 and December 31, 2013, respectively.

[2] Total loans held for investment includes deferred loan fees, net of deferred origination costs and unamortized purchase premiums, net of discounts as well as purchase accounting adjustments. These items resulted in a net decrease in loan balances of $2.2 billion as of June 30, 2014 and a net increase in loan balances of $122.6 million as of December 31, 2013, respectively. The significant fluctuation between periods is due to the purchase accounting marks resulting from the Change in Control of SCUSA.

[3] Credit scores updated quarterly.

[4] Retail installment contracts and auto loans excludes $89.4 million and $0.0 million of LHFS at June 30, 2014 and December 31, 2013, respectively.

[5] Other consumer primarily includes recreational vehicles and marine loans.

[6] Commercial and industrial loans excluded $41.1 million and $17.9 million of LHFS at June 30, 2014 and December 31, 2013, respectively.

[7] Middle markets commercial real estate excluded $11.2 million and $0.0 million of LHFS at June 30, 2014 and December 31, 2013, respectively.