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Significant Transactions (FCC Spectrum Auction) (Details) - FCC Spectrum Auction [Member] - USD ($)
$ in Millions
 1 Months Ended
Sep. 30, 2016
Jul. 31, 2017
Apr. 13, 2017
FCC Spectrum Auction [Line Items]      
Deposit to acquire intangible asset $ 1,800    
Amount of spectrum acquired     $ 1,700
Subsequent Event [Member]      
FCC Spectrum Auction [Line Items]      
Proceeds from FCC Spectrum Auction   $ 482  
Subsequent Event [Member] | NBCUniversal Media LLC [Member]      
FCC Spectrum Auction [Line Items]      
Proceeds from FCC Spectrum Auction   $ 482