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Contingent Liabilities (Details) - USD ($)
$ in Millions
May 20, 2016
Mar. 31, 2018
Loss Contingencies [Line Items]    
Accrued environmental loss liabilities   $ 39
Energy Transfer Merger [Member]    
Loss Contingencies [Line Items]    
Loss contingency, damages sought, value $ 1,480  
Gas Pipeline [Member]    
Loss Contingencies [Line Items]    
Accrued environmental loss liabilities   7
Natural Gas Underground Storage Facilities [Member]    
Loss Contingencies [Line Items]    
Accrued environmental loss liabilities   10
Former Operations [Member]    
Loss Contingencies [Line Items]    
Accrued environmental loss liabilities   22
Maximum [Member] | Former Alaska Refinery [Member]    
Loss Contingencies [Line Items]    
Loss contingency, range of possible loss   $ 32