Quarterly report pursuant to Section 13 or 15(d)

Assets and Liabilities Measured at Fair Value (Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details)

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Assets and Liabilities Measured at Fair Value (Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) - USD ($)
$ in Millions
 9 Months Ended
Sep. 30, 2018
Mar. 09, 2018
Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Cash equivalents $ 389   $ 655
Equity Securities 282   2,275
Indemnification asset 100 $ 281  
Debt 1,426   1,846
Indemnification payment from GCI Liberty, Inc. 133    
Fair Value, Inputs, Level 1      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Cash equivalents 389   655
Equity Securities 282   2,275
Significant Other Observable Inputs (Level 2)      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Indemnification asset 100    
Debt $ 1,426   $ 1,846
1.75% Exchangeable Senior Debentures due 2046      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Interest rate (as a percent) 1.75%    
Securities repurchased 417,759    
Debt Instrument, Repurchase Amount $ 457    
Exchangeable debenture securities outstanding 332,241    
1.75% Exchangeable Senior Debentures due 2046 | GCI Liberty      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Indemnification payment from GCI Liberty, Inc. $ 133