Condensed Consolidating Financial Information (Condensed Consolidating Balance Sheet) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Assets
Cash and cash equivalents	$ 5,500	$ 3,814
Receivables, net	11,292	11,104
Programming rights	3,877	3,746
Other current assets	4,723	3,184
Total current assets	25,392	21,848
Film and television costs	8,933	7,837
Investments	6,989	7,883
Investment securing collateralized obligation	694	0
Investments in and amounts due from subsidiaries eliminated upon consolidation	0	0
Property and equipment, net	48,322	44,437
Goodwill	68,725	66,154	$ 36,780
Franchise rights	59,365	59,365
Other intangible assets, net	36,128	38,358
Other noncurrent assets, net	8,866	5,802
Total assets	263,414	251,684
Liabilities and Equity
Accounts payable and accrued expenses related to trade creditors	10,826	8,494
Accrued participations and residuals	1,730	1,808
Deferred revenue	2,768	2,182
Accrued expenses and other current liabilities	10,516	10,721
Current portion of long-term debt	4,452	4,398
Total current liabilities	30,292	27,603
Long-term debt, less current portion	97,765	107,345
Collateralized obligation	5,166	0
Deferred income taxes	28,180	27,589
Other noncurrent liabilities	16,765	15,329
Redeemable noncontrolling interests and redeemable subsidiary preferred stock	1,372	1,316
Equity:
Common stock	54	54
Other shareholders’ equity	82,672	71,559
Total Comcast Corporation shareholders’ equity	82,726	71,613
Noncontrolling interests	1,148	889
Total equity	83,874	72,502	$ 69,459
Total liabilities and equity	263,414	251,684
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
Investment securing collateralized obligation	0
Investments in and amounts due from subsidiaries eliminated upon consolidation	(600,866)	(586,231)
Property and equipment, net	0	0
Goodwill	0	0
Franchise rights	0	0
Other intangible assets, net	0	0
Other noncurrent assets, net	(535)	(458)
Total assets	(601,401)	(586,689)
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
Collateralized obligation	0
Deferred income taxes	(535)	(524)
Other noncurrent liabilities	0	66
Redeemable noncontrolling interests and redeemable subsidiary preferred stock	0	0
Equity:
Common stock	0	0
Other shareholders’ equity	(600,866)	(586,231)
Total Comcast Corporation shareholders’ equity	(600,866)	(586,231)
Noncontrolling interests	0	0
Total equity	(600,866)	(586,231)
Total liabilities and equity	(601,401)	(586,689)
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	115	66
Total current assets	115	66
Film and television costs	0	0
Investments	270	270
Investment securing collateralized obligation	0
Investments in and amounts due from subsidiaries eliminated upon consolidation	164,754	157,264
Property and equipment, net	660	670
Goodwill	0	0
Franchise rights	0	0
Other intangible assets, net	9	11
Other noncurrent assets, net	1,058	1,057
Total assets	166,866	159,338
Liabilities and Equity
Accounts payable and accrued expenses related to trade creditors	58	2
Accrued participations and residuals	0	0
Deferred revenue	0	0
Accrued expenses and other current liabilities	2,333	2,357
Current portion of long-term debt	2,731	699
Total current liabilities	5,122	3,058
Long-term debt, less current portion	75,786	81,661
Collateralized obligation	0
Deferred income taxes	0	0
Other noncurrent liabilities	3,232	3,006
Redeemable noncontrolling interests and redeemable subsidiary preferred stock	0	0
Equity:
Common stock	54	54
Other shareholders’ equity	82,672	71,559
Total Comcast Corporation shareholders’ equity	82,726	71,613
Noncontrolling interests	0	0
Total equity	82,726	71,613
Total liabilities and equity	166,866	159,338
Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Assets
Cash and cash equivalents	5,084	3,398
Receivables, net	11,292	11,104
Programming rights	3,877	3,746
Other current assets	4,565	3,070
Total current assets	24,818	21,318
Film and television costs	8,933	7,837
Investments	5,466	6,669
Investment securing collateralized obligation	694
Investments in and amounts due from subsidiaries eliminated upon consolidation	92,925	97,872
Property and equipment, net	47,662	43,767
Goodwill	68,725	66,154
Franchise rights	59,365	59,365
Other intangible assets, net	36,119	38,347
Other noncurrent assets, net	7,919	4,910
Total assets	352,626	346,239
Liabilities and Equity
Accounts payable and accrued expenses related to trade creditors	10,768	8,492
Accrued participations and residuals	1,730	1,808
Deferred revenue	2,768	2,182
Accrued expenses and other current liabilities	7,170	7,572
Current portion of long-term debt	1,714	3,695
Total current liabilities	24,150	23,749
Long-term debt, less current portion	13,973	15,690
Collateralized obligation	5,166
Deferred income taxes	28,298	27,734
Other noncurrent liabilities	11,754	11,056
Redeemable noncontrolling interests and redeemable subsidiary preferred stock	1,372	1,316
Equity:
Common stock	0	0
Other shareholders’ equity	266,765	265,805
Total Comcast Corporation shareholders’ equity	266,765	265,805
Noncontrolling interests	1,148	889
Total equity	267,913	266,694
Total liabilities and equity	352,626	346,239
Comcast Holdings [Member] | Subsidiary Issuer [Member] | Reportable Legal Entities [Member]
Assets
Cash and cash equivalents	0	0
Receivables, net	0	0
Programming rights	0	0
Other current assets	19	20
Total current assets	19	20
Film and television costs	0	0
Investments	12	11
Investment securing collateralized obligation	0
Investments in and amounts due from subsidiaries eliminated upon consolidation	152,179	147,028
Property and equipment, net	0	0
Goodwill	0	0
Franchise rights	0	0
Other intangible assets, net	0	0
Other noncurrent assets, net	327	208
Total assets	152,537	147,267
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	245	150
Current portion of long-term debt	0	0
Total current liabilities	245	150
Long-term debt, less current portion	154	146
Collateralized obligation	0
Deferred income taxes	350	314
Other noncurrent liabilities	145	0
Redeemable noncontrolling interests and redeemable subsidiary preferred stock	0	0
Equity:
Common stock	0	0
Other shareholders’ equity	151,643	146,657
Total Comcast Corporation shareholders’ equity	151,643	146,657
Noncontrolling interests	0	0
Total equity	151,643	146,657
Total liabilities and equity	152,537	147,267
CCCL Parent [Member] | Guarantor Subsidiaries [Member] | Reportable Legal Entities [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	156	143
Investment securing collateralized obligation	0
Investments in and amounts due from subsidiaries eliminated upon consolidation	135,536	130,214
Property and equipment, net	0	0
Goodwill	0	0
Franchise rights	0	0
Other intangible assets, net	0	0
Other noncurrent assets, net	0	0
Total assets	135,692	130,357
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	388	360
Current portion of long-term debt	0	0
Total current liabilities	388	360
Long-term debt, less current portion	2,100	2,100
Collateralized obligation	0
Deferred income taxes	0	0
Other noncurrent liabilities	0	0
Redeemable noncontrolling interests and redeemable subsidiary preferred stock	0	0
Equity:
Common stock	0	0
Other shareholders’ equity	133,204	127,897
Total Comcast Corporation shareholders’ equity	133,204	127,897
Noncontrolling interests	0	0
Total equity	133,204	127,897
Total liabilities and equity	135,692	130,357
NBCUniversal Media Parent [Member] | Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Assets
Cash and cash equivalents	416	416
Receivables, net	0	0
Programming rights	0	0
Other current assets	24	28
Total current assets	440	444
Film and television costs	0	0
Investments	1,085	790
Investment securing collateralized obligation	0
Investments in and amounts due from subsidiaries eliminated upon consolidation	55,472	53,853
Property and equipment, net	0	0
Goodwill	0	0
Franchise rights	0	0
Other intangible assets, net	0	0
Other noncurrent assets, net	97	85
Total assets	57,094	55,172
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	380	282
Current portion of long-term debt	7	4
Total current liabilities	387	286
Long-term debt, less current portion	5,752	7,748
Collateralized obligation	0
Deferred income taxes	67	65
Other noncurrent liabilities	1,634	1,201
Redeemable noncontrolling interests and redeemable subsidiary preferred stock	0	0
Equity:
Common stock	0	0
Other shareholders’ equity	49,254	45,872
Total Comcast Corporation shareholders’ equity	49,254	45,872
Noncontrolling interests	0	0
Total equity	49,254	45,872
Total liabilities and equity	$ 57,094	$ 55,172