Condensed Consolidating Financial Information (Condensed Consolidating Balance Sheet) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Assets
Cash and cash equivalents	$ 3,814	$ 3,428
Receivables, net	11,104	8,834
Programming rights	3,746	1,613
Other current assets	3,184	2,468
Total current assets	21,848	16,343
Film and television costs	7,837	7,087
Investments	7,883	6,931
Investments in and amounts due from subsidiaries eliminated upon consolidation	0	0
Property and equipment, net	44,437	38,470
Franchise rights	59,365	59,364
Goodwill	66,154	36,780	$ 35,980
Other intangible assets, net	38,358	18,133
Other noncurrent assets, net	5,802	4,354
Total assets	251,684	187,462
Liabilities and Equity
Accounts payable and accrued expenses related to trade creditors	8,494	6,908
Accrued participations and residuals	1,808	1,644
Deferred revenue	2,182	1,687
Accrued expenses and other current liabilities	10,721	6,620
Current portion of long-term debt	4,398	5,134
Total current liabilities	27,603	21,993
Long-term debt, less current portion	107,345	59,422
Deferred income taxes	27,589	24,259
Other noncurrent liabilities	15,329	10,972
Redeemable noncontrolling interests	1,316	1,357
Equity:
Common stock	54	55
Other shareholders’ equity	71,559	68,561
Total Comcast Corporation shareholders’ equity	71,613	68,616
Noncontrolling interests	889	843
Total equity	72,502	69,459	$ 56,163	$ 53,978
Total liabilities and equity	251,684	187,462
Elimination and Consolidation Adjustments [Member]
Assets
Cash and cash equivalents	0	0
Receivables, net	0	0
Programming rights	0	0
Other current assets	0	0
Total current assets	0	0
Film and television costs	0	0
Investments	0	0
Investments in and amounts due from subsidiaries eliminated upon consolidation	(586,231)	(562,645)
Property and equipment, net	0	0
Franchise rights	0	0
Goodwill	0	0
Other intangible assets, net	0	0
Other noncurrent assets, net	(458)	(314)
Total assets	(586,689)	(562,959)
Liabilities and Equity
Accounts payable and accrued expenses related to trade creditors	0	0
Accrued participations and residuals	0	0
Deferred revenue	0	0
Accrued expenses and other current liabilities	0	0
Current portion of long-term debt	0	0
Total current liabilities	0	0
Long-term debt, less current portion	0	0
Deferred income taxes	(524)	(343)
Other noncurrent liabilities	66	29
Redeemable noncontrolling interests	0	0
Equity:
Common stock	0	0
Other shareholders’ equity	(586,231)	(562,645)
Total Comcast Corporation shareholders’ equity	(586,231)	(562,645)
Noncontrolling interests	0	0
Total equity	(586,231)	(562,645)
Total liabilities and equity	(586,689)	(562,959)
Comcast Parent [Member] | Reportable Legal Entities [Member]
Assets
Cash and cash equivalents	0	0
Receivables, net	0	0
Programming rights	0	0
Other current assets	66	60
Total current assets	66	60
Film and television costs	0	0
Investments	270	146
Investments in and amounts due from subsidiaries eliminated upon consolidation	157,264	117,164
Property and equipment, net	670	551
Franchise rights	0	0
Goodwill	0	0
Other intangible assets, net	11	12
Other noncurrent assets, net	1,057	435
Total assets	159,338	118,368
Liabilities and Equity
Accounts payable and accrued expenses related to trade creditors	2	16
Accrued participations and residuals	0	0
Deferred revenue	0	0
Accrued expenses and other current liabilities	2,357	1,888
Current portion of long-term debt	699	2,810
Total current liabilities	3,058	4,714
Long-term debt, less current portion	81,661	42,428
Deferred income taxes	0	0
Other noncurrent liabilities	3,006	2,610
Redeemable noncontrolling interests	0	0
Equity:
Common stock	54	55
Other shareholders’ equity	71,559	68,561
Total Comcast Corporation shareholders’ equity	71,613	68,616
Noncontrolling interests	0	0
Total equity	71,613	68,616
Total liabilities and equity	159,338	118,368
Subsidiary Issuer [Member] | Reportable Legal Entities [Member] | Comcast Holdings [Member]
Assets
Cash and cash equivalents	0	0
Receivables, net	0	0
Programming rights	0	0
Other current assets	20	0
Total current assets	20	0
Film and television costs	0	0
Investments	11	21
Investments in and amounts due from subsidiaries eliminated upon consolidation	147,028	142,519
Property and equipment, net	0	0
Franchise rights	0	0
Goodwill	0	0
Other intangible assets, net	0	0
Other noncurrent assets, net	208	708
Total assets	147,267	143,248
Liabilities and Equity
Accounts payable and accrued expenses related to trade creditors	0	0
Accrued participations and residuals	0	0
Deferred revenue	0	0
Accrued expenses and other current liabilities	150	92
Current portion of long-term debt	0	0
Total current liabilities	150	92
Long-term debt, less current portion	146	140
Deferred income taxes	314	285
Other noncurrent liabilities	0	0
Redeemable noncontrolling interests	0	0
Equity:
Common stock	0	0
Other shareholders’ equity	146,657	142,731
Total Comcast Corporation shareholders’ equity	146,657	142,731
Noncontrolling interests	0	0
Total equity	146,657	142,731
Total liabilities and equity	147,267	143,248
Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member] | CCCL Parent [Member]
Assets
Cash and cash equivalents	0	0
Receivables, net	0	0
Programming rights	0	0
Other current assets	0	7
Total current assets	0	7
Film and television costs	0	0
Investments	143	108
Investments in and amounts due from subsidiaries eliminated upon consolidation	130,214	139,528
Property and equipment, net	0	0
Franchise rights	0	0
Goodwill	0	0
Other intangible assets, net	0	0
Other noncurrent assets, net	0	0
Total assets	130,357	139,643
Liabilities and Equity
Accounts payable and accrued expenses related to trade creditors	0	0
Accrued participations and residuals	0	0
Deferred revenue	0	0
Accrued expenses and other current liabilities	360	333
Current portion of long-term debt	0	0
Total current liabilities	360	333
Long-term debt, less current portion	2,100	2,100
Deferred income taxes	0	0
Other noncurrent liabilities	0	0
Redeemable noncontrolling interests	0	0
Equity:
Common stock	0	0
Other shareholders’ equity	127,897	137,210
Total Comcast Corporation shareholders’ equity	127,897	137,210
Noncontrolling interests	0	0
Total equity	127,897	137,210
Total liabilities and equity	130,357	139,643
Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member] | NBCUniversal Media Parent [Member]
Assets
Cash and cash equivalents	416	496
Receivables, net	0	0
Programming rights	0	0
Other current assets	28	25
Total current assets	444	521
Film and television costs	0	0
Investments	790	693
Investments in and amounts due from subsidiaries eliminated upon consolidation	53,853	50,102
Property and equipment, net	0	0
Franchise rights	0	0
Goodwill	0	0
Other intangible assets, net	0	0
Other noncurrent assets, net	85	88
Total assets	55,172	51,404
Liabilities and Equity
Accounts payable and accrued expenses related to trade creditors	0	0
Accrued participations and residuals	0	0
Deferred revenue	0	0
Accrued expenses and other current liabilities	282	326
Current portion of long-term debt	4	4
Total current liabilities	286	330
Long-term debt, less current portion	7,748	7,751
Deferred income taxes	65	67
Other noncurrent liabilities	1,201	1,128
Redeemable noncontrolling interests	0	0
Equity:
Common stock	0	0
Other shareholders’ equity	45,872	42,128
Total Comcast Corporation shareholders’ equity	45,872	42,128
Noncontrolling interests	0	0
Total equity	45,872	42,128
Total liabilities and equity	55,172	51,404
Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Assets
Cash and cash equivalents	3,398	2,932
Receivables, net	11,104	8,834
Programming rights	3,746	1,613
Other current assets	3,070	2,376
Total current assets	21,318	15,755
Film and television costs	7,837	7,087
Investments	6,669	5,963
Investments in and amounts due from subsidiaries eliminated upon consolidation	97,872	113,332
Property and equipment, net	43,767	37,919
Franchise rights	59,365	59,364
Goodwill	66,154	36,780
Other intangible assets, net	38,347	18,121
Other noncurrent assets, net	4,910	3,437
Total assets	346,239	297,758
Liabilities and Equity
Accounts payable and accrued expenses related to trade creditors	8,492	6,892
Accrued participations and residuals	1,808	1,644
Deferred revenue	2,182	1,687
Accrued expenses and other current liabilities	7,572	3,981
Current portion of long-term debt	3,695	2,320
Total current liabilities	23,749	16,524
Long-term debt, less current portion	15,690	7,003
Deferred income taxes	27,734	24,250
Other noncurrent liabilities	11,056	7,205
Redeemable noncontrolling interests	1,316	1,357
Equity:
Common stock	0	0
Other shareholders’ equity	265,805	240,576
Total Comcast Corporation shareholders’ equity	265,805	240,576
Noncontrolling interests	889	843
Total equity	266,694	241,419
Total liabilities and equity	$ 346,239	$ 297,758