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Related Party Transactions (Details) - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Dec. 31, 2018
Related Party Transaction [Line Items]      
Cash distributions $ 1,200 $ 1,100  
Related Party Transaction Revenue with Affiliates 37 34  
Related Party Transaction Expenditures from Transactions with Related Party $ 93 89  
Equity Method Investments and Joint Ventures [Abstract]      
Ownership Percentage in TTX Company 17.30%    
Investments related to TTX $ 620   $ 609
Parent Company      
Related Party Transaction [Line Items]      
Cash distributions 1,200 1,100  
Tax payments to parent company   $ 0  
Payable to parent company 253   21
Earliest Tax Year [Member] | Parent Company      
Related Party Transaction [Line Items]      
Tax payable to parent related to prior year tax audits $ 34   $ 33