LOANS AND ALLOWANCE FOR CREDIT LOSSES (Impaired Loans) (Details) (USD $)	9 Months Ended		12 Months Ended
	Sep. 30, 2014		Dec. 31, 2013
Loans and Leases Receivable Disclosure [Abstract]
Minimum amount for commercial non-accrual loans	$ 1,000,000
Financing Receivable, Impaired [Line Items]
Impaired financing receivable, recorded investment	2,433,811,000	[1]	1,233,152,000	[1]
Impaired financing receivable, unpaid principal balance	2,258,423,000		1,430,588,000
Impaired financing receivable, related specific reserves	107,064,000		225,796,000
Impaired financing receivables, average recorded investment	1,833,485,000		1,233,152,000
Commercial [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivable, recorded investment	404,252,000	[1]	479,343,000	[1]
Impaired financing receivable, unpaid principal balance	294,746,000		602,093,000
Impaired financing receivable, related specific reserves	73,723,000		90,594,000
Impaired financing receivables, average recorded investment	441,799,000		479,343,000
Corporate banking [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivable with no related allowance recorded, recorded investment	45,848,000	[1]	43,485,000	[1]
Impaired financing receivable with related allowance recorded, recorded investment	53,115,000	[1]	53,762,000	[1]
Impaired financing receivable with no related allowance recorded, unpaid principal balance	33,759,000		30,131,000
Impaired financing receivable with related allowance recorded, unpaid principal balance	46,452,000		52,100,000
Impaired financing receivable, related specific reserves	21,185,000		10,298,000
Impaired financing receivable with no related allowance recorded, average recorded investment	44,667,000		43,485,000
Impaired financing receivable with related allowance recorded, average recorded investment	53,439,000		53,762,000
Middle market commercial real estate [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivable with no related allowance recorded, recorded investment	119,975,000	[1]	101,137,000	[1]
Impaired financing receivable with related allowance recorded, recorded investment	84,995,000	[1]	118,845,000	[1]
Impaired financing receivable with no related allowance recorded, unpaid principal balance	68,363,000		128,874,000
Impaired financing receivable with related allowance recorded, unpaid principal balance	64,231,000		185,649,000
Impaired financing receivable, related specific reserves	20,056,000		26,130,000
Impaired financing receivable with no related allowance recorded, average recorded investment	110,556,000		101,137,000
Impaired financing receivable with related allowance recorded, average recorded investment	101,920,000		118,845,000
Santander real estate capital [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivable with no related allowance recorded, recorded investment	3,027,000	[1]	751,000	[1]
Impaired financing receivable with related allowance recorded, recorded investment	1,802,000	[1]	9,382,000	[1]
Impaired financing receivable with no related allowance recorded, unpaid principal balance	3,027,000		751,000
Impaired financing receivable with related allowance recorded, unpaid principal balance	556,000		8,136,000
Impaired financing receivable, related specific reserves	161,000		1,701,000
Impaired financing receivable with no related allowance recorded, average recorded investment	1,889,000		751,000
Impaired financing receivable with related allowance recorded, average recorded investment	5,592,000		9,382,000
Commercial and industrial loans [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivable with no related allowance recorded, recorded investment	6,172,000	[1]	13,131,000	[1]
Impaired financing receivable with related allowance recorded, recorded investment	55,264,000	[1]	100,224,000	[1]
Impaired financing receivable with no related allowance recorded, unpaid principal balance	6,172,000		42,512,000
Impaired financing receivable with related allowance recorded, unpaid principal balance	39,266,000		118,276,000
Impaired financing receivable, related specific reserves	29,435,000		50,252,000
Impaired financing receivable with no related allowance recorded, average recorded investment	9,652,000		13,131,000
Impaired financing receivable with related allowance recorded, average recorded investment	77,744,000		100,224,000
Multi-family loans [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivable with no related allowance recorded, recorded investment	25,913,000	[1]	27,031,000	[1]
Impaired financing receivable with related allowance recorded, recorded investment	5,810,000	[1]	11,418,000	[1]
Impaired financing receivable with no related allowance recorded, unpaid principal balance	25,913,000		27,031,000
Impaired financing receivable with related allowance recorded, unpaid principal balance	4,745,000		8,456,000
Impaired financing receivable, related specific reserves	1,417,000		2,201,000
Impaired financing receivable with no related allowance recorded, average recorded investment	26,472,000		27,031,000
Impaired financing receivable with related allowance recorded, average recorded investment	8,614,000		11,418,000
Other commercial [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivable with no related allowance recorded, recorded investment	110,000	[1]	0	[1]
Impaired financing receivable with related allowance recorded, recorded investment	2,221,000	[1]	177,000	[1]
Impaired financing receivable with no related allowance recorded, unpaid principal balance	110,000		0
Impaired financing receivable with related allowance recorded, unpaid principal balance	2,152,000		177,000
Impaired financing receivable, related specific reserves	1,469,000		12,000
Impaired financing receivable with no related allowance recorded, average recorded investment	55,000		0
Impaired financing receivable with related allowance recorded, average recorded investment	1,199,000		177,000
Consumer [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivable, recorded investment	2,029,559,000	[1]	753,809,000	[1]
Impaired financing receivable, unpaid principal balance	1,963,677,000		828,495,000
Impaired financing receivable, related specific reserves	33,341,000		135,202,000
Impaired financing receivables, average recorded investment	1,391,686,000		753,809,000
Residential mortgages [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivable with no related allowance recorded, recorded investment	24,883,000	[1]	92,143,000	[1]
Impaired financing receivable with related allowance recorded, recorded investment	104,178,000	[1]	547,329,000	[1]
Impaired financing receivable with no related allowance recorded, unpaid principal balance	24,883,000		92,143,000
Impaired financing receivable with related allowance recorded, unpaid principal balance	78,601,000		603,866,000
Impaired financing receivable, related specific reserves	24,517,000		124,746,000
Impaired financing receivable with no related allowance recorded, average recorded investment	58,513,000		92,143,000
Impaired financing receivable with related allowance recorded, average recorded investment	325,754,000		547,329,000
Home equity loans and lines of credit [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivable with no related allowance recorded, recorded investment	28,222,000	[1]	31,074,000	[1]
Impaired financing receivable with related allowance recorded, recorded investment	55,552,000	[1]	54,900,000	[1]
Impaired financing receivable with no related allowance recorded, unpaid principal balance	28,222,000		31,074,000
Impaired financing receivable with related allowance recorded, unpaid principal balance	47,089,000		63,975,000
Impaired financing receivable, related specific reserves	4,374,000		5,479,000
Impaired financing receivable with no related allowance recorded, average recorded investment	29,648,000		31,074,000
Impaired financing receivable with related allowance recorded, average recorded investment	55,226,000		54,900,000
Retail installment contracts and auto loans [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivable with no related allowance recorded, recorded investment	64,569,000	[1]	0	[1]
Impaired financing receivable with related allowance recorded, recorded investment	1,700,507,000	[1]	0	[1]
Impaired financing receivable with no related allowance recorded, unpaid principal balance	45,895,000		0
Impaired financing receivable with related allowance recorded, unpaid principal balance	1,693,304,000		0
Impaired financing receivable, related specific reserves	647,000		0
Impaired financing receivable with no related allowance recorded, average recorded investment	32,285,000		0
Impaired financing receivable with related allowance recorded, average recorded investment	850,254,000		0
Personal unsecured loan [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivable with no related allowance recorded, recorded investment	31,540,000	[1]	0	[1]
Impaired financing receivable with related allowance recorded, recorded investment	1,296,000	[1]	2,535,000	[1]
Impaired financing receivable with no related allowance recorded, unpaid principal balance	31,540,000		0
Impaired financing receivable with related allowance recorded, unpaid principal balance	1,296,000		2,535,000
Impaired financing receivable, related specific reserves	767,000		677,000
Impaired financing receivable with no related allowance recorded, average recorded investment	15,770,000		0
Impaired financing receivable with related allowance recorded, average recorded investment	1,916,000		2,535,000
Other consumer [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivable with no related allowance recorded, recorded investment	5,919,000	[1]	8,345,000	[1]
Impaired financing receivable with related allowance recorded, recorded investment	12,893,000	[1]	17,483,000	[1]
Impaired financing receivable with no related allowance recorded, unpaid principal balance	5,919,000		17,420,000
Impaired financing receivable with related allowance recorded, unpaid principal balance	6,928,000		17,482,000
Impaired financing receivable, related specific reserves	3,036,000		4,300,000
Impaired financing receivable with no related allowance recorded, average recorded investment	7,132,000		8,345,000
Impaired financing receivable with related allowance recorded, average recorded investment	$ 15,188,000		$ 17,483,000

[1] Recorded investment includes deferred loan fees, net of deferred origination costs and unamortized purchase premiums, net of discounts as well as purchase accounting adjustments.