Condensed Consolidating Financial Information (Condensed Consolidating Balance Sheet) (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Assets
Cash and cash equivalents	$ 3,507	$ 3,814
Receivables, net	10,684	11,104
Programming rights	3,457	3,746
Other current assets	4,675	3,184
Total current assets	22,323	21,848
Film and television costs	8,647	7,837
Investments	7,473	7,883
Investment securing collateralized obligation	816	0
Investments in and amounts due from subsidiaries eliminated upon consolidation	0	0
Property and equipment, net	46,790	44,437
Franchise rights	59,365	59,365
Goodwill	66,913	66,154
Other intangible assets, net	35,164	38,358
Other noncurrent assets, net	8,883	5,802
Total assets	256,374	251,684
Liabilities and Equity
Accounts payable and accrued expenses related to trade creditors	10,198	8,494
Accrued participations and residuals	1,615	1,808
Deferred revenue	2,944	2,182
Accrued expenses and other current liabilities	10,193	10,721
Current portion of long-term debt	1,039	4,398
Total current liabilities	25,989	27,603
Long-term debt, less current portion	99,847	107,345
Collateralized obligation	5,165	0
Deferred income taxes	27,992	27,589
Other noncurrent liabilities	16,853	15,329
Redeemable noncontrolling interests	1,368	1,316
Equity:
Common stock	54	54
Other shareholders’ equity	78,090	71,559
Total Comcast Corporation shareholders’ equity	78,144	71,613
Noncontrolling interests	1,016	889
Total equity	79,160	72,502	$ 72,345
Total liabilities and equity	256,374	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	(593,909)	(586,231)
Property and equipment, net	0	0
Franchise rights	0	0
Goodwill	0	0
Other intangible assets, net	0	0
Other noncurrent assets, net	(417)	(458)
Total assets	(594,326)	(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	(562)	(524)
Other noncurrent liabilities	145	66
Redeemable noncontrolling interests	0	0
Equity:
Common stock	0	0
Other shareholders’ equity	(593,909)	(586,231)
Total Comcast Corporation shareholders’ equity	(593,909)	(586,231)
Noncontrolling interests	0	0
Total equity	(593,909)	(586,231)
Total liabilities and equity	(594,326)	(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	128	66
Total current assets	128	66
Film and television costs	0	0
Investments	275	270
Investment securing collateralized obligation	0
Investments in and amounts due from subsidiaries eliminated upon consolidation	158,369	157,264
Property and equipment, net	664	670
Franchise rights	0	0
Goodwill	0	0
Other intangible assets, net	8	11
Other noncurrent assets, net	1,025	1,057
Total assets	160,469	159,338
Liabilities and Equity
Accounts payable and accrued expenses related to trade creditors	0	2
Accrued participations and residuals	0	0
Deferred revenue	0	0
Accrued expenses and other current liabilities	2,421	2,357
Current portion of long-term debt	0	699
Total current liabilities	2,421	3,058
Long-term debt, less current portion	76,654	81,661
Collateralized obligation	0
Deferred income taxes	0	0
Other noncurrent liabilities	3,250	3,006
Redeemable noncontrolling interests	0	0
Equity:
Common stock	54	54
Other shareholders’ equity	78,090	71,559
Total Comcast Corporation shareholders’ equity	78,144	71,613
Noncontrolling interests	0	0
Total equity	78,144	71,613
Total liabilities and equity	160,469	159,338
Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Assets
Cash and cash equivalents	3,233	3,398
Receivables, net	10,684	11,104
Programming rights	3,457	3,746
Other current assets	4,502	3,070
Total current assets	21,876	21,318
Film and television costs	8,647	7,837
Investments	5,988	6,669
Investment securing collateralized obligation	816
Investments in and amounts due from subsidiaries eliminated upon consolidation	98,744	97,872
Property and equipment, net	46,126	43,767
Franchise rights	59,365	59,365
Goodwill	66,913	66,154
Other intangible assets, net	35,156	38,347
Other noncurrent assets, net	8,014	4,910
Total assets	351,645	346,239
Liabilities and Equity
Accounts payable and accrued expenses related to trade creditors	10,198	8,492
Accrued participations and residuals	1,615	1,808
Deferred revenue	2,944	2,182
Accrued expenses and other current liabilities	6,857	7,572
Current portion of long-term debt	1,032	3,695
Total current liabilities	22,646	23,749
Long-term debt, less current portion	15,190	15,690
Collateralized obligation	5,165
Deferred income taxes	28,142	27,734
Other noncurrent liabilities	11,903	11,056
Redeemable noncontrolling interests	1,368	1,316
Equity:
Common stock	0	0
Other shareholders’ equity	266,215	265,805
Total Comcast Corporation shareholders’ equity	266,215	265,805
Noncontrolling interests	1,016	889
Total equity	267,231	266,694
Total liabilities and equity	351,645	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	22	20
Total current assets	22	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	149,186	147,028
Property and equipment, net	0	0
Franchise rights	0	0
Goodwill	0	0
Other intangible assets, net	0	0
Other noncurrent assets, net	166	208
Total assets	149,386	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	244	150
Current portion of long-term debt	0	0
Total current liabilities	244	150
Long-term debt, less current portion	152	146
Collateralized obligation	0
Deferred income taxes	344	314
Other noncurrent liabilities	0	0
Redeemable noncontrolling interests	0	0
Equity:
Common stock	0	0
Other shareholders’ equity	148,646	146,657
Total Comcast Corporation shareholders’ equity	148,646	146,657
Noncontrolling interests	0	0
Total equity	148,646	146,657
Total liabilities and equity	149,386	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	159	143
Investment securing collateralized obligation	0
Investments in and amounts due from subsidiaries eliminated upon consolidation	132,753	130,214
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	132,912	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	256	360
Current portion of long-term debt	0	0
Total current liabilities	256	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	0	0
Equity:
Common stock	0	0
Other shareholders’ equity	130,556	127,897
Total Comcast Corporation shareholders’ equity	130,556	127,897
Noncontrolling interests	0	0
Total equity	130,556	127,897
Total liabilities and equity	132,912	130,357
NBCUniversal Media Parent [Member] | Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Assets
Cash and cash equivalents	274	416
Receivables, net	0	0
Programming rights	0	0
Other current assets	23	28
Total current assets	297	444
Film and television costs	0	0
Investments	1,039	790
Investment securing collateralized obligation	0
Investments in and amounts due from subsidiaries eliminated upon consolidation	54,857	53,853
Property and equipment, net	0	0
Franchise rights	0	0
Goodwill	0	0
Other intangible assets, net	0	0
Other noncurrent assets, net	95	85
Total assets	56,288	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	415	282
Current portion of long-term debt	7	4
Total current liabilities	422	286
Long-term debt, less current portion	5,751	7,748
Collateralized obligation	0
Deferred income taxes	68	65
Other noncurrent liabilities	1,555	1,201
Redeemable noncontrolling interests	0	0
Equity:
Common stock	0	0
Other shareholders’ equity	48,492	45,872
Total Comcast Corporation shareholders’ equity	48,492	45,872
Noncontrolling interests	0	0
Total equity	48,492	45,872
Total liabilities and equity	$ 56,288	$ 55,172