Recent Accounting Pronouncements (Effect of Changes in Revenue Recognition - Statement of Income) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue	$ 27,846	$ 22,135	$ 21,735	$ 22,791	$ 22,075	$ 21,081	$ 21,286	$ 20,587	$ 94,507	$ 85,029	$ 80,736
Total costs and expenses									75,498	67,011	63,905
Operating income	4,514	4,836	5,014	4,645	4,129	4,779	4,568	4,542	19,009	18,018	16,831
Net Income Attributable to Comcast Corporation	$ 2,511	$ 2,886	$ 3,216	$ 3,118	$ 14,999	$ 2,642	$ 2,521	$ 2,573	11,731	22,735	8,678
NBCUniversal Media LLC [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue									35,895	32,950	31,398
Total costs and expenses									29,229	26,473	26,040
Operating income									6,666	6,477	5,358
Net Income Attributable to Comcast Corporation									$ 5,237	5,080	4,171
Previous Reported [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue										84,526	80,403
Total costs and expenses										66,539	63,544
Operating income										17,987	16,859
Net Income Attributable to Comcast Corporation										22,714	8,695
Previous Reported [Member] | NBCUniversal Media LLC [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue										32,997	31,593
Total costs and expenses										26,516	26,171
Operating income										6,481	5,422
Net Income Attributable to Comcast Corporation										5,084	4,235
Effects of Adoption [Member] | Accounting Standards Update 2014-09 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue										503	333
Total costs and expenses										472	361
Operating income										31	(28)
Net Income Attributable to Comcast Corporation										21	(17)
Effects of Adoption [Member] | Accounting Standards Update 2014-09 [Member] | NBCUniversal Media LLC [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue										(47)	(195)
Total costs and expenses										(43)	(131)
Operating income										(4)	(64)
Net Income Attributable to Comcast Corporation										$ (4)	$ (64)