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Property, Plant, and Equipment (Details ARO) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Asset Retirement Obligations    
Asset Retirement Obligations, Noncurrent $ 968 $ 946
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]    
Beginning balance 998 862
Liabilities incurred 21 33
Liabilities settled (19) (16)
Accretion expense 71 [1] 141
Revisions (1) [2] (39) (22)
Ending balance 1,032 $ 998
Asset Retirement Obligation Costs [Member]    
Unusual or Infrequent Item [Line Items]    
Transco's annual funding commitment for ARO $ 36  
[1] (1)The decrease in accretion expense in 2018 primarily reflects the absence of a 2017 adjustment associated with obligations identified from certain Transco land agreements.
[2] (2)Several factors are considered in the annual review process, including inflation rates, current estimates for removal cost, market risk premiums, discount rates, and the estimated remaining useful life of the assets. The 2018 revisions reflect changes in removal cost estimates, decreases in the estimated remaining useful life of certain assets and increases in the discount rates used in the annual review process. The 2017 revisions reflect changes in removal cost estimates and decreases in the estimated remaining useful life of certain assets and discount rates used in the annual review process.