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, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Tax Effect									$ (578,892)	$ (554,997)	$ (539,967)
Net Income Attributable to Common Shareholders	$ 237,400	$ 260,400	$ 230,700	$ 259,500	$ 229,200	$ 265,300	$ 203,600	$ 244,200	987,996	942,302	878,485
Defined Benefit Plan Costs:
Total Amounts Reclassified from AOCL, Net of Tax									(6,500)	(6,000)	(6,300)
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									1,300	1,400	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 Attributable to Common Shareholders									(2,000)	(2,100)	(2,100)
Amortization of Actuarial Losses
Defined Benefit Plan Costs:
Amortization of Actuarial Losses									6,200	5,600	6,600
Amortization of Prior Service Cost
Defined Benefit Plan Costs:
Amortization of Actuarial Losses									(1,100)	(800)	(200)
Defined Benefit Plans
Defined Benefit Plan Costs:
Amortization of Actuarial Losses									(7,300)	(6,400)	(6,800)
Tax Effect									2,800	2,500	2,600
Total Amounts Reclassified from AOCL, Net of Tax									(4,500)	(3,900)	(4,200)
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									$ (3,300)	$ (3,500)	$ (3,500)