Goodwill and Intangible Assets (Narrative) (Details)	12 Months Ended
	Dec. 31, 2019 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