BUSINESS SEGMENT INFORMATION (Segment Information) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Segment Reporting Information [Line Items]
Net interest income	$ 1,538,790	$ 1,621,725	$ 3,124,766	$ 3,224,610
Non-interest income	786,318	962,984	1,813,478	1,858,431
Credit loss expense	977,373	480,632	2,162,983	1,080,843
Total expenses	3,429,690	1,542,386	5,013,491	3,084,801
(LOSS)/INCOME BEFORE INCOME TAX (BENEFIT)/PROVISION	(2,081,955)	561,691	(2,238,230)	917,397
Intersegment revenue/(expense)	0	0	0	0
Total assets	152,353,787	143,910,431	152,353,787	143,910,431	$ 149,499,477
Reportable Segments | CBB
Segment Reporting Information [Line Items]
Net interest income	358,430	374,187	708,278	739,164
Non-interest income	71,373	86,543	154,926	161,200
Credit loss expense	186,714	40,215	352,184	77,215
Total expenses	1,955,547	404,102	2,340,820	794,073
(LOSS)/INCOME BEFORE INCOME TAX (BENEFIT)/PROVISION	(1,712,458)	16,413	(1,829,800)	29,076
Intersegment revenue/(expense)	541	581	961	976
Total assets	24,052,719	22,801,820	24,052,719	22,801,820
Reportable Segments | C&I
Segment Reporting Information [Line Items]
Net interest income	70,034	57,428	127,853	110,771
Non-interest income	12,221	16,738	25,952	33,010
Credit loss expense	36,568	6,925	71,178	15,585
Total expenses	337,287	59,508	387,037	114,183
(LOSS)/INCOME BEFORE INCOME TAX (BENEFIT)/PROVISION	(291,600)	7,733	(304,410)	14,013
Intersegment revenue/(expense)	2,381	1,053	4,944	2,304
Total assets	7,048,220	7,442,924	7,048,220	7,442,924
Reportable Segments | CRE & VF
Segment Reporting Information [Line Items]
Net interest income	90,160	105,148	191,309	207,714
Non-interest income	2,157	3,194	5,350	6,433
Credit loss expense	14,252	3,534	63,387	3,400
Total expenses	29,736	32,593	58,681	62,667
(LOSS)/INCOME BEFORE INCOME TAX (BENEFIT)/PROVISION	48,329	72,215	74,591	148,080
Intersegment revenue/(expense)	1,019	1,782	2,753	3,791
Total assets	19,567,288	18,809,753	19,567,288	18,809,753
Reportable Segments | CIB
Segment Reporting Information [Line Items]
Net interest income	42,457	40,033	79,376	78,068
Non-interest income	90,398	54,423	140,550	106,629
Credit loss expense	15,314	(4,188)	33,455	(2,746)
Total expenses	62,424	66,120	124,923	132,560
(LOSS)/INCOME BEFORE INCOME TAX (BENEFIT)/PROVISION	55,117	32,524	61,548	54,883
Intersegment revenue/(expense)	(3,941)	(3,401)	(8,658)	(7,071)
Total assets	12,419,110	10,178,060	12,419,110	10,178,060
Reportable Segments | Other
Segment Reporting Information [Line Items]
Net interest income	(9,330)	30,715	15,662	71,904
Non-interest income	(49,109)	114,251	65,244	206,633
Credit loss expense	(137,597)	4,622	(127,436)	8,393
Total expenses	121,796	181,599	291,186	406,301
(LOSS)/INCOME BEFORE INCOME TAX (BENEFIT)/PROVISION	(42,638)	(41,255)	(82,844)	(136,157)
Intersegment revenue/(expense)	0	(15)	0	0
Total assets	41,997,755	38,261,781	41,997,755	38,261,781
Reportable Segments | SC
Segment Reporting Information [Line Items]
Net interest income	984,745	992,485	1,996,152	1,976,050
Non-interest income	667,242	713,737	1,441,074	1,389,291
Credit loss expense	861,896	430,676	1,769,783	981,555
Total expenses	919,626	795,514	1,803,423	1,566,487
(LOSS)/INCOME BEFORE INCOME TAX (BENEFIT)/PROVISION	(129,535)	480,032	(135,980)	817,299
Intersegment revenue/(expense)	0	0	0	0
Total assets	47,268,695	46,416,093	47,268,695	46,416,093
SC Purchase Price Adjustments | SC
Segment Reporting Information [Line Items]
Net interest income	(201)	9,802	(423)	17,126
Non-interest income	3,168	2,313	5,021	4,314
Credit loss expense	226	(1,152)	432	(2,559)
Total expenses	9,804	9,860	19,593	20,390
(LOSS)/INCOME BEFORE INCOME TAX (BENEFIT)/PROVISION	(7,063)	3,407	(15,427)	3,609
Intersegment revenue/(expense)	0	0	0	0
Total assets	0	0	0	0
Eliminations
Segment Reporting Information [Line Items]
Net interest income	2,495	11,927	6,559	23,813
Non-interest income	(11,132)	(28,215)	(24,639)	(49,079)
Credit loss expense	0	0	0	0
Total expenses	(6,530)	(6,910)	(12,172)	(11,860)
(LOSS)/INCOME BEFORE INCOME TAX (BENEFIT)/PROVISION	(2,107)	(9,378)	(5,908)	(13,406)
Intersegment revenue/(expense)	0	0	0	0
Total assets	$ 0	$ 0	$ 0	$ 0