ACCUMULATED OTHER COMPREHENSIVE INCOME/(LOSS) - Schedule of Changes in AOCI By Component (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	$ 10,711,734	$ 10,352,215
OCI Before Reclassifications		(4,500)
Amounts Reclassified from AOCL		6,000
Net OCI		1,500
Ending balance	11,086,242	10,711,734
Total
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(65,282)	(66,844)
OCI Before Reclassifications	(7,600)
Amounts Reclassified from AOCL	6,500
Net OCI	(1,100)
Ending balance	(66,403)	(65,282)
Qualified Cash Flow Hedging Instruments
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(8,200)	(10,300)
OCI Before Reclassifications	0	0
Amounts Reclassified from AOCL	2,000	2,100
Net OCI	2,000	2,100
Ending balance	(6,200)	(8,200)
Unrealized Gains/(Losses) on Marketable Securities
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	400	(1,900)
OCI Before Reclassifications	(400)	2,300
Amounts Reclassified from AOCL	0	0
Net OCI	(400)	2,300
Ending balance	0	400
Defined Benefit Plans
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(57,500)	(54,600)
OCI Before Reclassifications	(7,200)	(6,800)
Amounts Reclassified from AOCL	4,500	3,900
Net OCI	(2,700)	(2,900)
Ending balance	$ (60,200)	$ (57,500)