COMMITMENTS AND CONTINGENCIES (Details) (USD $)	12 Months Ended		396 Months Ended
	Dec. 31, 2012 unions sites	Dec. 31, 2011	Dec. 31, 2012 unions sites
Loss Contingencies [Line Items]
Letter of credit provided	$ 210,000,000		$ 210,000,000
Monthly gas supply related demand charges and reservation fees	3,800,000
Estimated litigation liability	500,000	200,000	500,000
Percentage of personnel represented in collective bargaining agreements	62.00%		62.00%
Number of unions	2		2
Number of sites for environmental cleanup	12		12
Number of sites covered by insurance	11		11
Insurance policy limit	50,000,000		50,000,000
Accrual for Environmental Loss Contingencies [Roll Forward]
Beginning of Year	89,984,000	87,393,000
Accruals	26,552,000	21,880,000	304,800,000
Expenditures	(9,126,000)	(19,289,000)	(197,400,000)
End of Year	107,410,000	89,984,000	107,410,000
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	107,400,000		107,400,000
Range of possible loss, maximum	225,700,000		225,700,000
Environmental Restoration Costs [Member] | Sites Comprising the Majority the Environmental Remediation [Member]
Accrual for Environmental Loss Contingencies [Roll Forward]
Range of possible loss, minimum	90,700,000		90,700,000
Range of possible loss, maximum	$ 191,800,000		$ 191,800,000
Number of sites affected by environmental remediation	6		6