ACCUMULATED OTHER COMPREHENSIVE INCOME / (LOSS) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total other comprehensive income/(loss), pretax activity	$ (64,456)	$ 55,702	$ 403,154	$ 360,610
Total other comprehensive income/(loss), tax effect	2,443	(12,342)	(117,274)	(92,117)
TOTAL OTHER COMPREHENSIVE (LOSS) / GAIN, NET OF TAX	(62,013)	43,360	285,880	268,493
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	20,226,777	24,504,819	24,398,830	23,847,232
Net Activity	(62,013)	43,360	285,880	268,493
Ending balance	20,804,971	24,669,277	20,804,971	24,669,277
Accumulated Other Comprehensive Income / (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	259,686	(96,519)	(88,207)	(321,652)
Ending balance	197,673	(53,159)	197,673	(53,159)
Net unrealized gains on cash flow hedge derivative financial instruments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income/(loss), pretax activity	(34,921)	2,509	180,139	26,549
Other comprehensive income/(loss), tax effect	(4,073)	1,974	(63,520)	(10,361)
Other comprehensive income/(loss), net activity	(38,994)	4,483	116,619	16,188
Reclassification adjustment, pretax activity	274	5,293	411	235
Reclassification adjustment, tax effect	18	(1,559)	(79)	(69)
Reclassification adjustment, net activity	292	3,734	332	166
Total other comprehensive income/(loss), pretax activity	(34,647)	7,802	180,550	26,784
Total other comprehensive income/(loss), tax effect	(4,055)	415	(63,599)	(10,430)
TOTAL OTHER COMPREHENSIVE (LOSS) / GAIN, NET OF TAX	(38,702)	8,217	116,951	16,354
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	135,539	(11,676)	(20,114)	(19,813)
Net Activity	(38,702)	8,217	116,951	16,354
Ending balance	96,837	(3,459)	96,837	(3,459)
Net unrealized gains on investments in debt securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income/(loss), pretax activity	(15,446)	47,439	257,976	323,169
Other comprehensive income/(loss), tax effect	2,124	(12,642)	(70,309)	(81,798)
Other comprehensive income/(loss), net activity	(13,322)	34,797	187,667	241,371
Reclassification adjustment, pretax activity	(32,731)	(267)	(55,246)	(2,646)
Reclassification adjustment, tax effect	4,502	71	17,148	670
Reclassification adjustment, net activity	(28,229)	(196)	(38,098)	(1,976)
Total other comprehensive income/(loss), pretax activity	(48,177)	47,172	202,730	320,523
Total other comprehensive income/(loss), tax effect	6,626	(12,571)	(53,161)	(81,128)
TOTAL OTHER COMPREHENSIVE (LOSS) / GAIN, NET OF TAX	(41,551)	34,601	149,569	239,395
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	168,240	(40,973)	(22,880)	(245,767)
Net Activity	(41,551)	34,601	149,569	239,395
Ending balance	126,689	(6,372)	126,689	(6,372)
Pension and post-retirement actuarial gains
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total other comprehensive income/(loss), pretax activity	18,368	728	19,874	13,303
Total other comprehensive income/(loss), tax effect	(128)	(186)	(514)	(559)
TOTAL OTHER COMPREHENSIVE (LOSS) / GAIN, NET OF TAX	18,240	542	19,360	12,744
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(44,093)	(43,870)	(45,213)	(56,072)
Net Activity	18,240	542	19,360	12,744
Ending balance	$ (25,853)	$ (43,328)	$ (25,853)	$ (43,328)