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Significant Transactions (FCC Spectrum Auction) (Details) - FCC Spectrum [Member] - USD ($)
$ in Millions
1 Months Ended 12 Months Ended
Jul. 31, 2017
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2019
Dec. 31, 2018
Jun. 30, 2017
FCC Spectrum Auction [Line Items]            
Proceeds from FCC spectrum auction $ 482          
Gain on sale of spectrum rights   $ 337        
Amount of spectrum acquired       $ 2,337 $ 2,333 $ 1,700
Deposit to acquire intangible asset     $ 1,800      
NBCUniversal Media LLC [Member]            
FCC Spectrum Auction [Line Items]            
Proceeds from FCC spectrum auction $ 482          
Gain on sale of spectrum rights   $ 337        
Amount of spectrum acquired       $ 612 $ 608