ACCUMULATED OTHER COMPREHENSIVE INCOME/(LOSS) - Schedule of Changes in AOCI By Component (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	$ 12,629,994	$ 11,486,817
OCI Before Reclassifications	(19,200)	(12,100)
Amounts Reclassified from AOCI	7,900	7,000
Net OCI	(11,300)	(5,100)
Ending balance	14,063,566	12,629,994
Total
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(65,059)	(60,000)
Ending balance	(76,411)	(65,059)
Qualified Cash Flow Hedging Instruments
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(3,000)	(4,400)
OCI Before Reclassifications	0	0
Amounts Reclassified from AOCI	1,600	1,400
Net OCI	1,600	1,400
Ending balance	(1,400)	(3,000)
Unrealized Gains on Marketable Securities
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	700	(500)
OCI Before Reclassifications	400	1,200
Amounts Reclassified from AOCI	0	0
Net OCI	400	1,200
Ending balance	1,100	700
Defined Benefit Plans
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(62,800)	(55,100)
OCI Before Reclassifications	(19,600)	(13,300)
Amounts Reclassified from AOCI	6,300	5,600
Net OCI	(13,300)	(7,700)
Ending balance	$ (76,100)	$ (62,800)