LOANS AND ALLOWANCE FOR CREDIT LOSSES (Lending Asset Quality Indicators) (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014		Dec. 31, 2013
Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 35,054,313	[1]	$ 32,169,154	[1]
Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	33,408,531	[1]	30,426,898	[1]
Commercial [Member] | Special mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	720,849	[1]	640,834	[1]
Commercial [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	812,374	[1]	977,431	[1]
Commercial [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	112,559	[1]	123,991	[1]
Corporate banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,412,053		3,767,870
Corporate banking [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,078,566		3,385,253
Corporate banking [Member] | Special mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	108,295		106,001
Corporate banking [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	191,152		260,122
Corporate banking [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	34,040		16,494
Middle market commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,611,134		3,510,372
Middle market commercial real estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,242,055		3,068,667
Middle market commercial real estate [Member] | Special mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	126,373		62,062
Middle market commercial real estate [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	188,143		310,318
Middle market commercial real estate [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	54,563		69,325
Santander real estate capital [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,885,808		2,025,644
Santander real estate capital [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,660,988		1,779,544
Santander real estate capital [Member] | Special mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	123,044		112,257
Santander real estate capital [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	101,002		132,999
Santander real estate capital [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	774		844
Commercial and industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	14,995,490		12,838,348
Commercial and industrial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	14,413,266		12,320,254
Commercial and industrial [Member] | Special mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	299,606		283,939
Commercial and industrial [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	260,582		202,347
Commercial and industrial [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	22,036		31,808
Multi-family [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	9,229,611		8,237,029
Multi-family [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	9,106,009		8,109,023
Multi-family [Member] | Special mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	59,858		59,379
Multi-family [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	63,215		63,284
Multi-family [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	529		5,343
Remaining commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,920,217		1,789,891
Remaining commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,907,647		1,764,157
Remaining commercial [Member] | Special mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,673		17,196
Remaining commercial [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	8,280		8,361
Remaining commercial [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	617		177
Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	40,873,982	[1]	17,881,472	[1]
Consumer [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	39,423,444	[1]	17,255,401	[1]
Consumer [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,450,538	[1]	626,071	[1]
Residential mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	9,651,706		9,672,204
Residential mortgages [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	9,203,457		9,198,639
Residential mortgages [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	448,249		473,565
Home equity loans and lines of credit [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	6,190,475		6,311,694
Home equity loans and lines of credit [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	6,046,688		6,203,419
Home equity loans and lines of credit [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	143,787		108,275
Retail installment contracts and auto loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	21,712,938		81,804
Retail installment contracts and auto loans [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	20,895,954		79,936
Retail installment contracts and auto loans [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	816,984		1,868
Personal unsecured loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,861,805		493,785
Personal unsecured loan [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,829,220		493,785
Personal unsecured loan [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	32,585		0
Other consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,457,058		1,321,985
Other consumer [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,448,125		1,279,622
Other consumer [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 8,933		$ 42,363

[1] Financing receivables include LHFS.