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DEBT - Other (Details) - USD ($)
$ in Millions
9 Months Ended
Sep. 30, 2017
Dec. 31, 2016
Other Fixed-Rate and Variable-Rate Debt Disclosures    
Estimated fair value of long-term debt $ 4,100 $ 4,900
Debt carrying value 5,139 5,268
Letter of Credit | Revolving Credit Facility    
Other Variable-Rate Debt Disclosures    
Aggregate letters of credit issued $ 137 $ 130
Pro Forma | Credit Facilities    
Other Variable-Rate Debt Disclosures    
Percentage of change in the variable interest rates 0.125%  
Effect of 1/8 percent change in annual interest expense $ 3