v3.10.0.1
Goodwill and Intangible Assets (Narrative) (Details)
12 Months Ended
Dec. 31, 2018
segment
division
NBCUniversal Media LLC [Member]  
Segment Reporting Information [Line Items]  
Number of reportable segments 4
Software [Member]  
Segment Reporting Information [Line Items]  
Finite-lived intangible asset amortization period 5 years
Software [Member] | NBCUniversal Media LLC [Member]  
Segment Reporting Information [Line Items]  
Finite-lived intangible asset amortization period 5 years
Maximum [Member] | Software [Member]  
Segment Reporting Information [Line Items]  
Finite-lived intangible asset amortization period 5 years
Maximum [Member] | Software [Member] | NBCUniversal Media LLC [Member]  
Segment Reporting Information [Line Items]  
Finite-lived intangible asset amortization period 5 years
Cable Communications [Member]  
Segment Reporting Information [Line Items]  
Number of reportable segments 1
Cable Communications [Member] | Operating Segments [Member]  
Segment Reporting Information [Line Items]  
Number of divisions | division 3