ACCUMULATED OTHER COMPREHENSIVE INCOME/(LOSS) - Schedule of Amounts Reclassified From AOCI By Component (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Tax Effect									$ (288,972)	$ (578,892)	$ (554,997)
Net Income/(Loss) Attributable to Common Shareholders	$ 231,300	$ 289,400	$ 242,800	$ 269,500	$ 237,400	$ 260,400	$ 230,700	$ 259,500	1,033,000	987,996	942,302
Defined Benefit Plan Costs:
Total Amounts Reclassified from AOCI, Net of Tax									6,600	6,500	6,000
Accumulated Net Gain (Loss) from Cash Flow Hedges Including Portion Attributable to Noncontrolling Interest | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Tax Effect									1,000	1,300	1,400
Qualified Cash Flow Hedging Instruments, Net of Tax | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net Income/(Loss) Attributable to Common Shareholders									(1,800)	(2,000)	(2,100)
Amortization of Actuarial Losses
Defined Benefit Plan Costs:
Reclassifications from AOCI									(6,000)	(6,200)	(5,600)
Amortization of Prior Service Cost
Defined Benefit Plan Costs:
Reclassifications from AOCI									(400)	(1,100)	(800)
Defined Benefit Plans
Defined Benefit Plan Costs:
Reclassifications from AOCI									(6,400)	(7,300)	(6,400)
Tax Effect									1,600	2,800	2,500
Total Amounts Reclassified from AOCI, Net of Tax									(4,800)	(4,500)	(3,900)
Interest Expense | Accumulated Net Gain (Loss) from Cash Flow Hedges Including Portion Attributable to Noncontrolling Interest | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Qualified Cash Flow Hedging Instruments									$ (2,800)	$ (3,300)	$ (3,500)