Condensed Consolidating Financial Information (Condensed Consolidating Balance Sheet) (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018
Assets
Cash and cash equivalents	$ 3,919	$ 3,814
Receivables, net	10,835	11,104
Programming rights	1,947	3,746
Other current assets	4,660	3,184
Total current assets	21,361	21,848
Film and television costs	8,553	7,837
Investments	8,438	7,883
Investments in and amounts due from subsidiaries eliminated upon consolidation	0	0
Property and equipment, net	46,047	44,437
Franchise rights	59,365	59,365
Goodwill	67,945	66,154
Other intangible assets, net	36,076	38,358
Other noncurrent assets, net	8,770	5,802
Total assets	256,555	251,684
Liabilities and Equity
Accounts payable and accrued expenses related to trade creditors	10,014	8,494
Accrued participations and residuals	1,683	1,808
Deferred revenue	2,642	2,182
Accrued expenses and other current liabilities	10,304	10,721
Current portion of long-term debt	6,365	4,398
Total current liabilities	31,008	27,603
Long-term debt, less current portion	101,248	107,345
Deferred income taxes	27,996	27,589
Other noncurrent liabilities	17,144	15,329
Redeemable noncontrolling interests	1,329	1,316
Equity:
Common stock	54	54
Other shareholders’ equity	76,796	71,559
Total Comcast Corporation shareholders’ equity	76,850	71,613
Noncontrolling interests	980	889
Total equity	77,830	72,502	$ 71,743
Total liabilities and equity	256,555	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
Investments in and amounts due from subsidiaries eliminated upon consolidation	(593,569)	(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	(467)	(458)
Total assets	(594,036)	(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
Deferred income taxes	(612)	(524)
Other noncurrent liabilities	145	66
Redeemable noncontrolling interests	0	0
Equity:
Common stock	0	0
Other shareholders’ equity	(593,569)	(586,231)
Total Comcast Corporation shareholders’ equity	(593,569)	(586,231)
Noncontrolling interests	0	0
Total equity	(593,569)	(586,231)
Total liabilities and equity	(594,036)	(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	281	270
Investments in and amounts due from subsidiaries eliminated upon consolidation	160,659	157,264
Property and equipment, net	668	670
Franchise rights	0	0
Goodwill	0	0
Other intangible assets, net	10	11
Other noncurrent assets, net	1,038	1,057
Total assets	162,771	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	2,403	2,357
Current portion of long-term debt	2,587	699
Total current liabilities	4,990	3,058
Long-term debt, less current portion	77,782	81,661
Deferred income taxes	0	0
Other noncurrent liabilities	3,149	3,006
Redeemable noncontrolling interests	0	0
Equity:
Common stock	54	54
Other shareholders’ equity	76,796	71,559
Total Comcast Corporation shareholders’ equity	76,850	71,613
Noncontrolling interests	0	0
Total equity	76,850	71,613
Total liabilities and equity	162,771	159,338
Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Assets
Cash and cash equivalents	3,616	3,398
Receivables, net	10,835	11,104
Programming rights	1,947	3,746
Other current assets	4,501	3,070
Total current assets	20,899	21,318
Film and television costs	8,553	7,837
Investments	7,099	6,669
Investments in and amounts due from subsidiaries eliminated upon consolidation	98,426	97,872
Property and equipment, net	45,379	43,767
Franchise rights	59,365	59,365
Goodwill	67,945	66,154
Other intangible assets, net	36,066	38,347
Other noncurrent assets, net	7,935	4,910
Total assets	351,667	346,239
Liabilities and Equity
Accounts payable and accrued expenses related to trade creditors	10,014	8,492
Accrued participations and residuals	1,683	1,808
Deferred revenue	2,642	2,182
Accrued expenses and other current liabilities	6,913	7,572
Current portion of long-term debt	1,767	3,695
Total current liabilities	23,019	23,749
Long-term debt, less current portion	15,463	15,690
Deferred income taxes	28,206	27,734
Other noncurrent liabilities	12,303	11,056
Redeemable noncontrolling interests	1,329	1,316
Equity:
Common stock	0	0
Other shareholders’ equity	270,367	265,805
Total Comcast Corporation shareholders’ equity	270,367	265,805
Noncontrolling interests	980	889
Total equity	271,347	266,694
Total liabilities and equity	351,667	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
Investments in and amounts due from subsidiaries eliminated upon consolidation	147,775	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	163	208
Total assets	147,972	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
Deferred income taxes	334	314
Other noncurrent liabilities	0	0
Redeemable noncontrolling interests	0	0
Equity:
Common stock	0	0
Other shareholders’ equity	147,242	146,657
Total Comcast Corporation shareholders’ equity	147,242	146,657
Noncontrolling interests	0	0
Total equity	147,242	146,657
Total liabilities and equity	147,972	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	148	143
Investments in and amounts due from subsidiaries eliminated upon consolidation	130,444	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	130,592	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	356	360
Current portion of long-term debt	0	0
Total current liabilities	356	360
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	128,136	127,897
Total Comcast Corporation shareholders’ equity	128,136	127,897
Noncontrolling interests	0	0
Total equity	128,136	127,897
Total liabilities and equity	130,592	130,357
NBCUniversal Media Parent [Member] | Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Assets
Cash and cash equivalents	303	416
Receivables, net	0	0
Programming rights	0	0
Other current assets	22	28
Total current assets	325	444
Film and television costs	0	0
Investments	898	790
Investments in and amounts due from subsidiaries eliminated upon consolidation	56,265	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	101	85
Total assets	57,589	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	388	282
Current portion of long-term debt	2,011	4
Total current liabilities	2,399	286
Long-term debt, less current portion	5,751	7,748
Deferred income taxes	68	65
Other noncurrent liabilities	1,547	1,201
Redeemable noncontrolling interests	0	0
Equity:
Common stock	0	0
Other shareholders’ equity	47,824	45,872
Total Comcast Corporation shareholders’ equity	47,824	45,872
Noncontrolling interests	0	0
Total equity	47,824	45,872
Total liabilities and equity	$ 57,589	$ 55,172