Quarterly report pursuant to Section 13 or 15(d)

Investments In Available-For-Sale Securities And Other Cost Investments (Details)

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Investments In Available-For-Sale Securities And Other Cost Investments (Details) - USD ($)
$ in Millions
6 Months Ended 12 Months Ended
Jun. 09, 2017
Sep. 07, 2016
Jun. 30, 2017
Jun. 30, 2016
Dec. 31, 2017
Dec. 31, 2016
Transaction details [Line Items]            
Investments in available-for-sale securities and other cost investments     $ 750.0     $ 1,309.0
Accumulated Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax     0.0     0.0
Payments to Acquire Investments     442.0 $ 11.0    
Formula 1            
Transaction details [Line Items]            
Payments to Acquire Investments   $ 746.0        
Liberty Sirius XM Group            
Transaction details [Line Items]            
Investments in available-for-sale securities and other cost investments     173.0      
Payments to Acquire Investments     434.0      
Liberty Sirius XM Group | Pandora            
Transaction details [Line Items]            
Payments to Acquire Investments $ 172.5          
Liberty Sirius XM Group | Pandora | Fair Value Option Securities            
Transaction details [Line Items]            
Investments in available-for-sale securities and other cost investments     173.0      
Liberty Sirius XM Group | Pandora | Forecast            
Transaction details [Line Items]            
Payments to Acquire Investments         $ 480.0  
Ownership Interest In Investee         19.00%  
Ownership percentage on an as-converted basis         16.00%  
Braves Group            
Transaction details [Line Items]            
Investments in available-for-sale securities and other cost investments     8.0     8.0
Payments to Acquire Investments     2.0 8.0    
Braves Group | AFS and cost method investments            
Transaction details [Line Items]            
Investments in available-for-sale securities and other cost investments     8.0     8.0
Formula One Group            
Transaction details [Line Items]            
Investments in available-for-sale securities and other cost investments     569.0     1,301.0
Payments to Acquire Investments     6.0 $ 3.0    
Formula One Group | Fair Value Option Securities            
Transaction details [Line Items]            
Investments in available-for-sale securities and other cost investments     508.0     489.0
Formula One Group | AFS and cost method investments            
Transaction details [Line Items]            
Investments in available-for-sale securities and other cost investments     61.0     812.0
Formula One Group | Other equity securities | Fair Value Option Securities            
Transaction details [Line Items]            
Investments in available-for-sale securities and other cost investments     19.0     13.0
Formula One Group | Other AFS Equity Securities | AFS and cost method investments            
Transaction details [Line Items]            
Investments in available-for-sale securities and other cost investments     61.0     53.0
Formula One Group | Time Warner Inc | Fair Value Option Securities            
Transaction details [Line Items]            
Investments in available-for-sale securities and other cost investments     427.0     411.0
Formula One Group | Viacom, Inc. | Fair Value Option Securities            
Transaction details [Line Items]            
Investments in available-for-sale securities and other cost investments     $ 62.0     65.0
Formula One Group | Formula 1 | AFS and cost method investments            
Transaction details [Line Items]            
Investments in available-for-sale securities and other cost investments           $ 759.0