v3.10.0.1
Related Party Transactions (Narrative) (Details) - USD ($)
$ in Millions
1 Months Ended 3 Months Ended 12 Months Ended
Mar. 01, 2018
Oct. 31, 2017
Dec. 31, 2017
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Sep. 30, 2016
Related Party Transaction [Line Items]              
Other noncurrent liabilities     $ 10,972 $ 15,329 $ 10,972    
Interest expense on extinguishment of debt       3,542 3,086 $ 2,942  
Recognized share-based compensation expense       639 586 507  
Restricted share units [Member]              
Related Party Transaction [Line Items]              
Recognized share-based compensation expense       402 349 306  
Unrecognized pretax compensation expense on nonvested awards       $ 1,100      
Unrecognized pretax compensation expense on nonvested awards, weighted average period of recognition (in years)       1 year 7 months      
Stock options [Member]              
Related Party Transaction [Line Items]              
Recognized share-based compensation expense       $ 205 205 173  
Unrecognized pretax compensation expense on nonvested awards       $ 437      
Unrecognized pretax compensation expense on nonvested awards, weighted average period of recognition (in years)       1 year 8 months 12 days      
NBCUniversal Media LLC [Member]              
Related Party Transaction [Line Items]              
Other noncurrent liabilities     4,153 $ 5,177 4,153    
Interest expense on extinguishment of debt       489 727 595  
Recognized share-based compensation expense       151 133 $ 99  
NBCUniversal Media LLC [Member] | Restricted share units [Member]              
Related Party Transaction [Line Items]              
Unrecognized pretax compensation expense on nonvested awards       $ 270      
Unrecognized pretax compensation expense on nonvested awards, weighted average period of recognition (in years)       1 year 7 months      
NBCUniversal Media LLC [Member] | Stock options [Member]              
Related Party Transaction [Line Items]              
Unrecognized pretax compensation expense on nonvested awards       $ 23      
Unrecognized pretax compensation expense on nonvested awards, weighted average period of recognition (in years)       1 year      
NBCUniversal Media LLC [Member] | Carrying Value Of Related Party Contractual Obligation [Member]              
Related Party Transaction [Line Items]              
Other noncurrent liabilities       $ 383      
NBCUniversal Media LLC [Member] | NBCUniversal Holdings Preferred Stock [Member]              
Related Party Transaction [Line Items]              
Preferred stock, dividend rate       8.25%      
Preferred stock liquidation preference value       $ 9,400      
Preferred stock dividend rate, spread on variable rate 7.44%            
NBCUniversal Media LLC [Member] | Former Comcast And NBCUniversal Revolving Credit Agreements [Member]              
Related Party Transaction [Line Items]              
Revolving credit agreement capacity             $ 3,000
NBCUniversal Media LLC [Member] | Comcast and NBCUniversal Revolving Credit Agreements [Member]              
Related Party Transaction [Line Items]              
Revolving credit agreement capacity             $ 5,000
Borrowing margin for LIBOR based borrowings       1.00%      
Senior Notes Exchange [Member] | NBCUniversal Media LLC [Member]              
Related Party Transaction [Line Items]              
Interest expense on extinguishment of debt   $ 157          
Senior Notes Exchange [Member] | Senior Notes [Member] | Senior 3.97% Notes Due 2047 [Member] | NBCUniversal Media LLC [Member]              
Related Party Transaction [Line Items]              
Aggregate principal amount   $ 2,000          
Interest rate   3.97%          
Senior Notes Exchange [Member] | Senior Notes [Member] | Senior 4.00% Notes Due 2047 [Member] | NBCUniversal Media LLC [Member]              
Related Party Transaction [Line Items]              
Aggregate principal amount   $ 2,000          
Interest rate   4.00%          
Senior Notes Exchange [Member] | Senior Notes [Member] | Senior 4.00% Notes Due 2047 [Member] | Comcast [Member] | NBCUniversal Media LLC [Member]              
Related Party Transaction [Line Items]              
Aggregate principal amount   $ 610          
Interest rate   4.00%          
Senior Notes Exchange [Member] | Senior Notes [Member] | Senior 4.05% Notes Due 2052 [Member] | NBCUniversal Media LLC [Member]              
Related Party Transaction [Line Items]              
Aggregate principal amount   $ 1,500          
Interest rate   4.05%          
Senior Notes Exchange [Member] | Senior Notes [Member] | Comcast and NBCUniversal Senior Notes [Member]              
Related Party Transaction [Line Items]              
Aggregate principal amount     5,500   $ 5,500    
Amount of debt exchanged     $ 3,900        
Senior Notes Exchange [Member] | Senior Notes [Member] | Comcast and NBCUniversal Senior Notes [Member] | NBCUniversal Media LLC [Member]              
Related Party Transaction [Line Items]              
Amount of debt exchanged   $ 3,900          
Senior Notes Exchange [Member] | Senior Notes [Member] | Senior 6.40% Notes Due 2040 [Member] | NBCUniversal Media LLC [Member]              
Related Party Transaction [Line Items]              
Interest rate   6.40%          
Amount of debt exchanged   $ 442