COMMITMENTS AND CONTINGENCIES (Details) (USD $)	12 Months Ended		408 Months Ended
	Dec. 31, 2013 unions sites	Dec. 31, 2012 sites	Dec. 31, 2013 unions
Loss Contingencies [Line Items]
Letter of credit provided	$ 210,000,000		$ 210,000,000
Monthly gas supply related demand charges and reservation fees	4,000,000
Estimated litigation liability	500,000	500,000	500,000
Percentage of personnel represented in collective bargaining agreements	60.00%		60.00%
Number of unions	2		2
Number of sites for environmental cleanup		12
Number of sites covered by insurance		11
Insurance policy limit		50,000,000.0
Accrual for Environmental Loss Contingencies [Roll Forward]
Beginning of Year	107,410,000	89,984,000
Accruals	22,264,000	26,552,000	326,500,000
Expenditures	(10,182,000)	(9,126,000)	(207,000,000)
End of Year	119,492,000	107,410,000	119,492,000
Standby Letter of Credit [Member]
Loss Contingencies [Line Items]
Letter of credit provided	25,200,000		25,200,000
Environmental Restoration Costs [Member]
Accrual for Environmental Loss Contingencies [Roll Forward]
Range of possible loss, minimum	119,500,000		119,500,000
Range of possible loss, maximum	223,500,000		223,500,000
Environmental Restoration Costs [Member] | Sites Comprising the Majority the Environmental Remediation [Member]
Accrual for Environmental Loss Contingencies [Roll Forward]
Range of possible loss, minimum	100,400,000		100,400,000
Range of possible loss, maximum	$ 192,800,000		$ 192,800,000
Number of sites affected by environmental remediation	6		6