LOANS AND ALLOWANCE FOR CREDIT LOSSES (Troubled Debt Restructuring Activity) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2014 Contract		Jun. 30, 2013 Contract		Jun. 30, 2014 Contract		Jun. 30, 2013 Contract		Dec. 31, 2013
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings	$ 1,649,212				$ 1,649,212				$ 1,003,643
Trouble debt restructurings, number of contracts	80,428		124		93,263		302
Trouble debt restructurings, pre-modification outstanding recorded investment	982,364	[1]	28,851	[1]	1,154,456	[1]	75,050	[1]
Trouble debt restructurings, post-modification outstanding recorded investment	920,627	[2]	29,249	[2]	1,089,769	[2]	74,247	[2]
Consumer [Member]
Financing Receivable, Modifications [Line Items]
Trouble debt restructurings, subsequent default, number of contracts	800		9		812		21
Trouble debt restructurings, subsequent default, recorded investment	10,497	[3]	1,015	[3]	12,412	[3]	4,185	[3]
Corporate banking [Member]
Financing Receivable, Modifications [Line Items]
Trouble debt restructurings, number of contracts	7				21		1
Trouble debt restructurings, pre-modification outstanding recorded investment	30,961	[1]			53,278	[1]	19,750	[1]
Trouble debt restructurings, post-modification outstanding recorded investment	30,328	[2]			52,041	[2]	18,767	[2]
Middle market commercial real estate [Member]
Financing Receivable, Modifications [Line Items]
Trouble debt restructurings, number of contracts	3		1		3		1
Trouble debt restructurings, pre-modification outstanding recorded investment	9,939	[1]	7,820	[1]	9,939	[1]	7,820
Trouble debt restructurings, post-modification outstanding recorded investment	6,828	[2]	7,820	[2]	6,828	[2]	7,820
Santander real estate capital [Member]
Financing Receivable, Modifications [Line Items]
Trouble debt restructurings, number of contracts	0		1		0		2
Trouble debt restructurings, pre-modification outstanding recorded investment	0	[1]	1,316	[1]	0	[1]	4,040	[1]
Trouble debt restructurings, post-modification outstanding recorded investment	0	[2]	1,352	[2]	0	[2]	3,540	[2]
Commercial and industrial [Member]
Financing Receivable, Modifications [Line Items]
Trouble debt restructurings, number of contracts	0				0
Trouble debt restructurings, pre-modification outstanding recorded investment	0	[1]			0	[1]
Trouble debt restructurings, post-modification outstanding recorded investment	0	[2]			0	[2]
Multi-family [Member]
Financing Receivable, Modifications [Line Items]
Trouble debt restructurings, number of contracts	0				0
Trouble debt restructurings, pre-modification outstanding recorded investment	0	[1]			0	[1]
Trouble debt restructurings, post-modification outstanding recorded investment	0	[2]			0	[2]
Other commercial [Member]
Financing Receivable, Modifications [Line Items]
Trouble debt restructurings, number of contracts	2		2		3		7
Trouble debt restructurings, pre-modification outstanding recorded investment	549	[1]	1,078	[1]	1,046	[1]	2,790	[1]
Trouble debt restructurings, post-modification outstanding recorded investment	527	[2]	1,022	[2]	1,027	[2]	2,718	[2]
Residential mortgages [Member]
Financing Receivable, Modifications [Line Items]
Trouble debt restructurings, number of contracts	78	[4]	90	[4]	157	[4]	182	[4]
Trouble debt restructurings, pre-modification outstanding recorded investment	10,922	[1],[4]	16,060	[1],[4]	28,733	[1],[4]	31,863	[1],[4]
Trouble debt restructurings, post-modification outstanding recorded investment	11,396	[2],[4]	16,475	[2],[4]	29,066	[2],[4]	32,607	[2],[4]
Trouble debt restructurings, subsequent default, number of contracts	9		4		21		14
Trouble debt restructurings, subsequent default, recorded investment	779	[3]	618	[3]	2,694	[3]	3,412	[3]
Home equity loans and lines of credit [Member]
Financing Receivable, Modifications [Line Items]
Trouble debt restructurings, number of contracts	28		30		54		109
Trouble debt restructurings, pre-modification outstanding recorded investment	2,893	[1]	2,577	[1]	5,178	[1]	8,787	[1]
Trouble debt restructurings, post-modification outstanding recorded investment	2,893	[2]	2,580	[2]	5,178	[2]	8,795	[2]
Trouble debt restructurings, subsequent default, number of contracts	2		5		2		7
Trouble debt restructurings, subsequent default, recorded investment	312	[3]	397	[3]	312	[3]	773	[3]
Retail installment contracts and auto loans [Member]
Financing Receivable, Modifications [Line Items]
Trouble debt restructurings, number of contracts	56,059				68,773
Trouble debt restructurings, pre-modification outstanding recorded investment	911,882	[1]			1,041,023	[1]
Trouble debt restructurings, post-modification outstanding recorded investment	853,530	[2]			980,462	[2]
Trouble debt restructurings, subsequent default, number of contracts	788		0		788		0
Trouble debt restructurings, subsequent default, recorded investment	9,379	[3]	0	[3]	9,379	[3]	0	[3]
Personal unsecured loan [Member]
Financing Receivable, Modifications [Line Items]
Trouble debt restructurings, number of contracts	24,247				24,247
Trouble debt restructurings, pre-modification outstanding recorded investment	14,847	[1]			14,847	[1]
Trouble debt restructurings, post-modification outstanding recorded investment	14,754	[2]			14,754	[2]
Other consumer [Member]
Financing Receivable, Modifications [Line Items]
Trouble debt restructurings, number of contracts	4				5
Trouble debt restructurings, pre-modification outstanding recorded investment	371	[1]			412	[1]
Trouble debt restructurings, post-modification outstanding recorded investment	371	[2]			413	[2]
Trouble debt restructurings, subsequent default, number of contracts					1		0
Trouble debt restructurings, subsequent default, recorded investment					27	[3]	0	[3]
Performing [Member]
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings	1,292,488				1,292,488				656,606
Nonperforming [Member]
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings	$ 356,724				$ 356,724				$ 347,037

[1] Pre-modification outstanding recorded investment amount is the month-end balance prior to the month the modification occurred.

[2] Post-modification outstanding recorded investment amount is the month-end balance for the month that the modification occurred.

[3] The recorded investment represents the period-end balance at June 30, 2014 and 2013. Does not include Chapter 7 bankruptcy TDRs.

[4] The post-modification outstanding recorded investment amounts for residential mortgages exclude interest reserves.