BENEFIT PLANS (Components of Net Periodic Benefit Cost, Amounts Recognized in Other Comprehensive Income, Weighted-Average Assumptions) (Details) (USD $)	1 Months Ended	12 Months Ended
	Mar. 31, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Components of Net Periodic Benefit Cost
Service cost		$ 4,157,000	$ 21,904,000
Interest cost		44,392,000	40,995,000
Defined Benefit Plan, Assumed Health Care Cost Trend Rates [Abstract]
Healthcare cost trend rate assumed for next year		7.50%
Rate to which the cost trend rate gradually declines		5.00%
Year that the rate reaches the rate it is assumed to maintain		2025
Weighted-average assumptions used to determine net periodic benefit cost for years ended December 31
Expected return on plan assets		7.50%
Pension Plans, Defined Benefit
Components of Net Periodic Benefit Cost
Service cost		4,157,000	21,904,000	22,349,000
Interest cost		44,392,000	40,995,000	43,194,000
Expected return on plan assets		(50,802,000)	(47,425,000)	(48,780,000)
Curtailment (gain) loss		0	855,000	0
Amortization of prior service cost (credit)		188,000	339,000	274,000
Amortization of actuarial loss		11,221,000	20,429,000	19,526,000
Net periodic pension benefit cost		9,156,000	37,097,000	36,563,000
Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income
Net actuarial loss (gain)		118,915,000	(163,205,000)	63,981,000
Prior service cost (credit)		0	(583,000)	1,286,000
Pretax reclassification from AOCI included in net periodic postretirement benefit cost		(11,221,000)	(20,429,000)	(19,526,000)
Reclassification of prior service cost to net periodic pension benefit cost		(188,000)	(1,194,000)	(274,000)
Amount recognized in other comprehensive income		107,506,000	(185,411,000)	45,467,000
Amount recognized in net periodic pension benefit cost and other comprehensive income		116,662,000	(148,314,000)	82,030,000
Weighted-average assumptions used to determine net periodic benefit cost for years ended December 31
Discount rate		4.91%	4.33%	4.96%
Expected return on plan assets		7.50%	7.50%	8.00%
Rate of compensation increase (for salary-related plans)		3.50%	3.50%	3.50%
Weighted-average assumptions used to determine benefit obligation at December 31
Discount rate		4.14%	4.91%	4.19%
Rate of compensation increase (for salary-related plans)		3.70%	3.50%	3.50%
Other Postretirement Benefit Plans, Defined Benefit
Components of Net Periodic Benefit Cost
Service cost		2,146,000	2,830,000	4,409,000
Interest cost		3,297,000	3,260,000	5,851,000
Curtailment (gain) loss	(3,832,000)	(3,832,000)	0	0
Amortization of prior service cost (credit)		(4,327,000)	(4,863,000)	(1,372,000)
Amortization of actuarial loss		227,000	1,372,000	1,346,000
Net periodic pension benefit cost		(2,489,000)	2,599,000	10,234,000
Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income
Net actuarial loss (gain)		(5,256,000)	(20,444,000)	13,562,000
Prior service cost (credit)		0	0	(38,414,000)
Pretax reclassification from AOCI included in net periodic postretirement benefit cost		(227,000)	(1,372,000)	(1,346,000)
Reclassification of prior service cost to net periodic pension benefit cost		8,159,000	4,863,000	1,372,000
Amount recognized in other comprehensive income		2,676,000	(16,953,000)	(24,826,000)
Amount recognized in net periodic pension benefit cost and other comprehensive income		$ 187,000	$ (14,354,000)	$ (14,592,000)
Defined Benefit Plan, Assumed Health Care Cost Trend Rates [Abstract]
Healthcare cost trend rate assumed for next year		7.50%	7.50%	8.00%
Rate to which the cost trend rate gradually declines		5.00%	5.00%	5.00%
Year that the rate reaches the rate it is assumed to maintain		2025	2019	2019
Weighted-average assumptions used to determine net periodic benefit cost for years ended December 31
Discount rate		4.10%	3.30%	4.60%
Weighted-average assumptions used to determine benefit obligation at December 31
Discount rate		3.50%	4.10%	3.30%