ACCUMULATED OTHER COMPREHENSIVE INCOME / (LOSS) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total other comprehensive income/(loss), pretax activity	$ (12,680)	$ 166,951	$ 467,610	$ 304,908
Total other comprehensive income/(loss), tax effect	5,385	(46,437)	(119,717)	(79,775)
TOTAL OTHER COMPREHENSIVE (LOSS) / GAIN, NET OF TAX	(7,295)	120,514	347,893	225,133
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Equity, beginning balance	22,223,973	24,128,405	24,398,830	23,847,232
Net Activity	(7,295)	120,514	347,893	225,133
Equity, ending balance	20,226,777	24,504,820	20,226,777	24,504,820
Accumulated Other Comprehensive (Loss)/Income
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Equity, beginning balance	266,981	(217,033)	(88,207)	(321,652)
Equity, ending balance	259,686	(96,519)	259,686	(96,519)
Net unrealized gains on cash flow hedge derivative financial instruments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income/(loss), pretax activity	4,230	15,761	214,924	26,163
Other comprehensive income/(loss), tax effect	3,014	(10,969)	(59,482)	(12,971)
Other comprehensive income/(loss), net activity	7,244	4,792	155,442	13,192
Reclassification adjustment, pretax activity	137	(5,058)	273	(7,181)
Reclassification adjustment, tax effect	(33)	1,399	(62)	2,126
Reclassification adjustment, net activity	104	(3,659)	211	(5,055)
Total other comprehensive income/(loss), pretax activity	4,367	10,703	215,197	18,982
Total other comprehensive income/(loss), tax effect	2,981	(9,570)	(59,544)	(10,845)
TOTAL OTHER COMPREHENSIVE (LOSS) / GAIN, NET OF TAX	7,348	1,133	155,653	8,137
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Equity, beginning balance	128,191	(12,809)	(20,114)	(19,813)
Net Activity	7,348	1,133	155,653	8,137
Equity, ending balance	135,539	(11,676)	135,539	(11,676)
Net unrealized gains on investments in debt securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income/(loss), pretax activity	4,716	152,353	282,702	273,730
Other comprehensive income/(loss), tax effect	(688)	(37,266)	(67,363)	(68,652)
Other comprehensive income/(loss), net activity	4,028	115,087	215,339	205,078
Reclassification adjustment, pretax activity	(22,516)	(2,379)	(31,795)	(379)
Reclassification adjustment, tax effect	3,285	582	7,576	95
Reclassification adjustment, net activity	(19,231)	(1,797)	(24,219)	(284)
Total other comprehensive income/(loss), pretax activity	(17,800)	149,974	250,907	273,351
Total other comprehensive income/(loss), tax effect	2,597	(36,684)	(59,787)	(68,557)
TOTAL OTHER COMPREHENSIVE (LOSS) / GAIN, NET OF TAX	(15,203)	113,290	191,120	204,794
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Equity, beginning balance	183,443	(154,263)	(22,880)	(245,767)
Net Activity	(15,203)	113,290	191,120	204,794
Equity, ending balance	168,240	(40,973)	168,240	(40,973)
Pension and post-retirement actuarial gains
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total other comprehensive income/(loss), pretax activity	753	6,274	1,506	12,575
Total other comprehensive income/(loss), tax effect	(193)	(183)	(386)	(373)
TOTAL OTHER COMPREHENSIVE (LOSS) / GAIN, NET OF TAX	560	6,091	1,120	12,202
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Equity, beginning balance	(44,653)	(49,961)	(45,213)	(56,072)
Net Activity	560	6,091	1,120	12,202
Equity, ending balance	$ (44,093)	$ (43,870)	$ (44,093)	$ (43,870)