v3.10.0.1
Long-Term Debt (Narrative) (Details)
£ in Millions, $ in Millions, ¥ in Billions
1 Months Ended 3 Months Ended 6 Months Ended 12 Months Ended
Feb. 28, 2018
USD ($)
Dec. 31, 2018
USD ($)
Dec. 31, 2018
USD ($)
Dec. 31, 2018
GBP (£)
Dec. 31, 2018
USD ($)
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Dec. 31, 2018
GBP (£)
Dec. 31, 2018
JPY (¥)
Jun. 30, 2017
USD ($)
Debt Instrument [Line Items]                    
Fair value of debt   $ 114,100 $ 114,100   $ 114,100 $ 71,700        
Borrowings         44,781 11,466 $ 9,231      
Repayments of debt         8,798 6,364 3,052      
Amounts available under revolving credit facilities   9,200 9,200   9,200          
Unused irrevocable standby letters of credit   463 463   463          
NBCUniversal Media LLC [Member]                    
Debt Instrument [Line Items]                    
Fair value of debt   $ 13,200 $ 13,200   13,200 13,500        
Borrowings         692 3,948 0      
Repayments of debt         $ 438 3,498 $ 1,565      
Ownership in cable holding company subsidiaries   100.00% 100.00%   100.00%     100.00% 100.00%  
NBCUniversal Enterprise [Member]                    
Debt Instrument [Line Items]                    
Related party liquidation preference preferred stock not subject to guarantee   $ 725 $ 725   $ 725          
NBCUniversal Enterprise [Member] | NBCUniversal Media LLC [Member]                    
Debt Instrument [Line Items]                    
Related party aggregate principal amount senior notes not subject to guarantee   3,000 3,000   3,000          
Related party liquidation preference preferred stock not subject to guarantee   725 725   $ 725          
London Interbank Offered Rate (LIBOR) [Member]                    
Debt Instrument [Line Items]                    
Borrowing margin for LIBOR based borrowings         1.00%          
Senior Unsecured Fixed And Floating Rate Notes Issued October 2018 [Member]                    
Debt Instrument [Line Items]                    
Borrowings   27,000                
Senior Unsecured Fixed And Floating Rate Notes Issued October 2018 [Member] | NBCUniversal Media LLC [Member]                    
Debt Instrument [Line Items]                    
Aggregate principal amount   27,000 27,000   $ 27,000          
Comcast Revolving Credit Facility [Member]                    
Debt Instrument [Line Items]                    
Maximum borrowing capacity   7,600 7,600   7,600 7,000        
Potential increase of maximum borrowing capacity   10,000 10,000   10,000          
Amount outstanding under credit facility   0 0   0 0        
NBCUniversal Enterprise Credit Facility [Member]                    
Debt Instrument [Line Items]                    
Maximum borrowing capacity   1,600 1,600   1,600 1,500        
Potential increase of maximum borrowing capacity   2,000 2,000   2,000          
Amount outstanding under credit facility   0 0   0 0        
Amounts available under revolving credit facilities   942 942   942          
Universal Studios Japan Term Loan Maturing March 2022 [Member]                    
Debt Instrument [Line Items]                    
Guarantee obligations, term loans   3,500 3,500   3,500       ¥ 390  
Commercial Paper [Member]                    
Debt Instrument [Line Items]                    
Commercial paper capacity                   $ 7,000
Commercial paper outstanding   675 675   675 903        
NBCUniversal Enterprise Commercial Paper [Member]                    
Debt Instrument [Line Items]                    
Commercial paper capacity                   $ 1,500
Guarantor Subsidiaries [Member]                    
Debt Instrument [Line Items]                    
Principal amount of debt securities subject to guarantee   94,200 94,200   94,200          
Maturing In Next Five Years [Member]                    
Debt Instrument [Line Items]                    
Principal amount of debt securities subject to guarantee   26,900 26,900   26,900          
Senior Notes [Member]                    
Debt Instrument [Line Items]                    
Principal amount of debt securities subject to guarantee   3,000 3,000   3,000          
Comcast And Comcast Cable Debt Securities [Member] | NBCUniversal Media LLC [Member]                    
Debt Instrument [Line Items]                    
Principal amount of debt securities subject to guarantee   86,400 86,400   86,400          
Sky Revolving Credit Facility [Member]                    
Debt Instrument [Line Items]                    
Maximum borrowing capacity | £               £ 1,000    
Amount outstanding under credit facility   606 606   606     £ 475    
Amounts available under revolving credit facilities   670 670   670          
Sky Outstanding Indebtedness [Member]                    
Debt Instrument [Line Items]                    
Principal amount of debt securities not subject to guarantee   10,700 10,700   10,700          
Universal Beijing Resort Term Loans [Member]                    
Debt Instrument [Line Items]                    
Principal amount of debt securities not subject to guarantee   569 569   569          
Commercial Paper [Member] | NBCUniversal Enterprise [Member]                    
Debt Instrument [Line Items]                    
Commercial paper outstanding   675 675   675 0        
Commercial Paper [Member] | Comcast [Member]                    
Debt Instrument [Line Items]                    
Commercial paper outstanding   0 0   0 903        
Revolving Credit Facility [Member] | NBCUniversal Media LLC [Member]                    
Debt Instrument [Line Items]                    
Guarantee obligations, maximum capacity of credit facility   7,600 7,600   7,600          
Unsecured Debt [Member] | Comcast Unsecured Sterling-Denominated Term Loan Credit Agreement [Member]                    
Debt Instrument [Line Items]                    
Borrowings     8,700 £ 6,600            
Unsecured Debt [Member] | Unsecured Dollar-Denominated Term Loan Credit Agreement [Member]                    
Debt Instrument [Line Items]                    
Borrowings   3,000                
Unsecured Debt [Member] | Senior Unsecured Fixed Rate Notes Issued February 2018 [Member]                    
Debt Instrument [Line Items]                    
Borrowings $ 4,000                  
Cash Flow Hedging [Member] | Currency Swap [Member]                    
Debt Instrument [Line Items]                    
Aggregate notional amount   5,300 5,300   5,300 800        
Aggregate liability fair value   23 23   23 $ 80        
Net Investment Hedging [Member] | Currency Swap [Member]                    
Debt Instrument [Line Items]                    
Aggregate notional amount   $ 15,600 $ 15,600   $ 15,600