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DEBT (Details 2) - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2016
Dec. 31, 2015
Other Fixed-Rate and Variable-Rate Debt Disclosures    
Estimated fair value of long-term debt $ 3,000.0 $ 3,600.0
Debt carrying value 6,000.0 6,100.0
Letters of credit issued 61.0 70.0
Revolving credit facility | Letter of Credit    
Other Fixed-Rate and Variable-Rate Debt Disclosures    
Letters of credit issued $ 52.0 $ 49.0
Pro Forma    
Other Variable-Rate Debt Disclosures    
Percentage of change in the variable interest rates 0.125%  
Effect of 1/8 percent change in interest rates $ 2.1