LOANS AND ALLOWANCE FOR CREDIT LOSSES (Non-performing Assets) (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Nonperforming Assets [Line Items]
Non-accrual loans	$ 1,747,983	$ 998,409
Other repossessed assets	142,730	3,073
Total non-performing assets	112,512,985	77,144,021
Nonperforming [Member]
Nonperforming Assets [Line Items]
Other real estate owned	85,458	88,603
Repossessed vehicles	141,305	0
Other repossessed assets	6,379	3,073
Total other real estate owned and other repossessed assets	233,142	91,676
Total non-performing assets	1,981,125	1,090,085
Commercial [Member]
Nonperforming Assets [Line Items]
Non-accrual loans	297,445	372,338
Consumer [Member]
Nonperforming Assets [Line Items]
Non-accrual loans	1,450,538	626,071
Commercial real estate loans [Member] | Corporate banking [Member]
Nonperforming Assets [Line Items]
Non-accrual loans	99,023	93,100
Commercial real estate loans [Member] | Middle market commercial real estate [Member]
Nonperforming Assets [Line Items]
Non-accrual loans	113,584	143,802
Commercial real estate loans [Member] | Santander real estate capital [Member]
Nonperforming Assets [Line Items]
Non-accrual loans	3,847	13,171
Commercial and industrial loans [Member]
Nonperforming Assets [Line Items]
Non-accrual loans	63,399	97,254
Multi-family loans [Member]
Nonperforming Assets [Line Items]
Non-accrual loans	14,115	21,371
Other commercial [Member]
Nonperforming Assets [Line Items]
Non-accrual loans	3,477	3,640
Residential mortgages [Member]
Nonperforming Assets [Line Items]
Non-accrual loans	448,249	473,566
Home equity loans and lines of credit [Member]
Nonperforming Assets [Line Items]
Non-accrual loans	143,787	141,961
Retail installment contracts and auto loans [Member]
Nonperforming Assets [Line Items]
Non-accrual loans	816,984	1,205
Personal unsecured loan [Member]
Nonperforming Assets [Line Items]
Non-accrual loans	32,585	0
Other consumer [Member]
Nonperforming Assets [Line Items]
Non-accrual loans	$ 8,933	$ 9,339