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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Entity [Line Items]        
Contract Liabilities, Contract Term 5 to 10 years      
Number Of Years Of Service Employees Must Work To Be Entitled To Postretirement Medical And Life Insurance Benefits       5 years
Impairment of equity investments $ 37,730 $ 0 $ 0  
Natural Gas Gathering And Processing        
Entity [Line Items]        
Impairment charges 362,300      
Goodwill, Impairment Loss 153,400      
Impairment charges - long lived and other assets 382,200      
Natural Gas Liquids        
Entity [Line Items]        
Impairment charges $ 71,600      
Venice Energy Services Company [Member] | Natural Gas Gathering And Processing        
Entity [Line Items]        
Net ownership percentage 10.20%      
Impairment of equity investments $ 30,500      
Impairment of equity investments - goodwill $ 22,300      
Chisholm Pipeline Company [Member] | Natural Gas Liquids        
Entity [Line Items]        
Net ownership percentage 50.00%      
Impairment of equity investments $ 7,200      
Northern Border Pipeline [Member]        
Entity [Line Items]        
Net ownership percentage 50.00%      
Northern Border Pipeline [Member] | Natural Gas Pipelines        
Entity [Line Items]        
Net ownership percentage 50.00%      
Roadrunner Gas Transmission [Member]        
Entity [Line Items]        
Net ownership percentage 50.00%      
Roadrunner Gas Transmission [Member] | Natural Gas Pipelines        
Entity [Line Items]        
Net ownership percentage 50.00%      
Overland Pass Pipeline Company [Member]        
Entity [Line Items]        
Net ownership percentage 50.00%      
Overland Pass Pipeline Company [Member] | Natural Gas Liquids        
Entity [Line Items]        
Net ownership percentage 50.00%