LOANS AND ALLOWANCE FOR CREDIT LOSSES (Non-accrual Loans and Age Analysis of Past Due Loans) (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014		Dec. 31, 2013		Jun. 30, 2013
Financing Receivable, Recorded Investments, Past Due [Line Items]
30-59 days past due	$ 2,256,709		$ 303,809
68-89 days past due	746,700		157,726
Greater than 90 days	849,191		683,859
Total past due	3,852,600		1,145,394
Current	72,075,695		48,905,232
Total financing receivables	75,928,295		50,050,626		50,352,595
Recorded investment greater than 90 days and accruing	88,777		2,545
Corporate banking [Member]
Financing Receivable, Recorded Investments, Past Due [Line Items]
30-59 days past due	14,694
68-89 days past due	5,122
Greater than 90 days	52,470
Total past due	72,286
Current	3,339,767
Total financing receivables	3,412,053	[1]
Recorded investment greater than 90 days and accruing	0
Middle market commercial real estate [Member]
Financing Receivable, Recorded Investments, Past Due [Line Items]
30-59 days past due	21,179
68-89 days past due	6,941
Greater than 90 days	63,369
Total past due	91,489
Current	3,519,645
Total financing receivables	3,611,134	[1]
Recorded investment greater than 90 days and accruing	0
Santander real estate capital [Member]
Financing Receivable, Recorded Investments, Past Due [Line Items]
30-59 days past due	0
68-89 days past due	0
Greater than 90 days	0
Total past due	0
Current	1,885,808
Total financing receivables	1,885,808	[1]
Recorded investment greater than 90 days and accruing	0
Commercial real estate loans [Member] | Corporate banking [Member]
Financing Receivable, Recorded Investments, Past Due [Line Items]
30-59 days past due			12,758
68-89 days past due			5,751
Greater than 90 days			57,503
Total past due			76,012
Current			3,691,858
Total financing receivables			3,767,870	[1]
Recorded investment greater than 90 days and accruing			0
Commercial real estate loans [Member] | Middle market commercial real estate [Member]
Financing Receivable, Recorded Investments, Past Due [Line Items]
30-59 days past due			5,980
68-89 days past due			13,897
Greater than 90 days			83,809
Total past due			103,686
Current			3,406,685
Total financing receivables			3,510,371	[1]
Recorded investment greater than 90 days and accruing			0
Commercial real estate loans [Member] | Santander real estate capital [Member]
Financing Receivable, Recorded Investments, Past Due [Line Items]
30-59 days past due			4,177
68-89 days past due			9,705
Greater than 90 days			0
Total past due			13,882
Current			2,011,762
Total financing receivables			2,025,644	[1]
Recorded investment greater than 90 days and accruing			0
Commercial and industrial loans [Member]
Financing Receivable, Recorded Investments, Past Due [Line Items]
30-59 days past due	12,650		15,966
68-89 days past due	8,754		4,310
Greater than 90 days	29,280		34,354
Total past due	50,684		54,630
Current	14,944,806		12,783,719
Total financing receivables	14,995,490	[1]	12,838,349
Recorded investment greater than 90 days and accruing	0		0
Multi-family loans [Member]
Financing Receivable, Recorded Investments, Past Due [Line Items]
30-59 days past due	10,100		2,039
68-89 days past due	3,012		5,235
Greater than 90 days	6,168		9,563
Total past due	19,280		16,837
Current	9,210,331		8,220,192
Total financing receivables	9,229,611	[1]	8,237,029
Recorded investment greater than 90 days and accruing	0		0
Other commercial [Member]
Financing Receivable, Recorded Investments, Past Due [Line Items]
30-59 days past due	1,913		3,412
68-89 days past due	635		182
Greater than 90 days	1,090		2,171
Total past due	3,638		5,765
Current	1,916,579		1,784,126
Total financing receivables	1,920,217	[1]	1,789,891	[1]
Recorded investment greater than 90 days and accruing	0		0
Residential mortgages [Member]
Financing Receivable, Recorded Investments, Past Due [Line Items]
30-59 days past due	160,129		185,630
68-89 days past due	70,094		86,563
Greater than 90 days	357,066		379,076
Total past due	587,289		651,269
Current	9,064,417		9,020,935
Total financing receivables	9,651,706	[1]	9,672,204	[1]
Recorded investment greater than 90 days and accruing	0		0
Home equity loans and lines of credit [Member]
Financing Receivable, Recorded Investments, Past Due [Line Items]
30-59 days past due	23,034		32,017
68-89 days past due	9,079		15,567
Greater than 90 days	81,281		80,551
Total past due	113,394		128,135
Current	6,077,081		6,183,559
Total financing receivables	6,190,475	[1]	6,311,694	[1]
Recorded investment greater than 90 days and accruing	0		0
Retail installment contracts and auto loans [Member]
Financing Receivable, Recorded Investments, Past Due [Line Items]
30-59 days past due	1,941,432		7,900
68-89 days past due	617,470		2,988
Greater than 90 days	200,918		1,205
Total past due	2,759,820		12,093
Current	18,953,118		69,711
Total financing receivables	21,712,938	[1]	81,804	[1]
Recorded investment greater than 90 days and accruing	0		0
Personal unsecured loan [Member]
Financing Receivable, Recorded Investments, Past Due [Line Items]
30-59 days past due	49,845		4,289
68-89 days past due	12,516		1,693
Greater than 90 days	28,544		4,536
Total past due	90,905		10,518
Current	1,770,900		483,267
Total financing receivables	1,861,805	[1]	493,785	[1]
Recorded investment greater than 90 days and accruing	88,777		2,545
Other consumer [Member]
Financing Receivable, Recorded Investments, Past Due [Line Items]
30-59 days past due	21,733		29,641
68-89 days past due	13,077		11,835
Greater than 90 days	29,005		31,091
Total past due	63,815		72,567
Current	1,393,243		1,249,418
Total financing receivables	1,457,058	[1]	1,321,985	[1]
Recorded investment greater than 90 days and accruing	$ 0		$ 0

[1] Financing receivables include LHFS.