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Investments (Marketable Equity Securities) (Details) - USD ($)
$ in Millions
1 Months Ended 12 Months Ended
Mar. 31, 2017
Mar. 31, 2017
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Schedule of Marketable Equity Securities [Line Items]          
Realized and unrealized gains (losses) on equity securities, net     $ 656 $ (187) $ (17)
Marketable equity securities     353 341  
Nonmarketable equity securities     1,896 1,805  
NBCUniversal Media LLC [Member]          
Schedule of Marketable Equity Securities [Line Items]          
Realized and unrealized gains (losses) on equity securities, net     466 (217) $ 0
Marketable equity securities     295 162  
Nonmarketable equity securities     804 811  
Snap [Member]          
Schedule of Marketable Equity Securities [Line Items]          
Payments to acquire marketable equity securities   $ 500      
Marketable equity securities, recognized realized gains (losses)     293    
Marketable equity securities, recognized unrealized gains (losses)       (268)  
Marketable equity securities       162  
Snap [Member] | NBCUniversal Media LLC [Member]          
Schedule of Marketable Equity Securities [Line Items]          
Contributions from member $ 662        
Marketable equity securities, recognized realized gains (losses)     293    
Marketable equity securities, recognized unrealized gains (losses)       (268)  
Marketable equity securities       162  
Peloton [Member]          
Schedule of Marketable Equity Securities [Line Items]          
Realized and unrealized gains (losses) on equity securities, net     184    
Marketable equity securities     294    
Nonmarketable equity securities       110  
Peloton [Member] | NBCUniversal Media LLC [Member]          
Schedule of Marketable Equity Securities [Line Items]          
Realized and unrealized gains (losses) on equity securities, net     184    
Marketable equity securities     $ 294    
Nonmarketable equity securities       $ 110