Condensed Consolidating Financial Information (Condensed Consolidating Balance Sheet) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Assets
Cash and cash equivalents	$ 3,498	$ 3,814
Receivables, net	10,736	11,104
Programming rights	2,942	3,746
Other current assets	3,097	3,184
Total current assets	20,273	21,848
Film and television costs	8,051	7,837
Investments	9,159	7,883
Investments in and amounts due from subsidiaries eliminated upon consolidation	0	0
Property and equipment, net	45,721	44,437
Franchise rights	59,365	59,365
Goodwill	68,073	66,154
Other intangible assets, net	36,902	38,358
Other noncurrent assets, net	8,645	5,802
Total assets	256,189	251,684
Liabilities and Equity
Accounts payable and accrued expenses related to trade creditors	10,232	8,494
Accrued participations and residuals	1,739	1,808
Deferred revenue	2,485	2,182
Accrued expenses and other current liabilities	8,832	10,721
Current portion of long-term debt	4,629	4,398
Total current liabilities	27,917	27,603
Long-term debt, less current portion	104,464	107,345
Deferred income taxes	27,819	27,589
Other noncurrent liabilities	18,811	15,329
Redeemable noncontrolling interests	1,316	1,316
Equity:
Common stock	54	54
Other shareholders’ equity	74,905	71,559
Total Comcast Corporation shareholders’ equity	74,959	71,613
Noncontrolling interests	903	889
Total equity	75,862	72,502	$ 70,710	$ 69,459
Total liabilities and equity	256,189	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	(590,849)	(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	(486)	(458)
Total assets	(591,335)	(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	(552)	(524)
Other noncurrent liabilities	66	66
Redeemable noncontrolling interests	0	0
Equity:
Common stock	0	0
Other shareholders’ equity	(590,849)	(586,231)
Total Comcast Corporation shareholders’ equity	(590,849)	(586,231)
Noncontrolling interests	0	0
Total equity	(590,849)	(586,231)
Total liabilities and equity	(591,335)	(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	72	66
Total current assets	72	66
Film and television costs	0	0
Investments	280	270
Investments in and amounts due from subsidiaries eliminated upon consolidation	158,868	157,264
Property and equipment, net	663	670
Franchise rights	0	0
Goodwill	0	0
Other intangible assets, net	10	11
Other noncurrent assets, net	1,163	1,057
Total assets	161,056	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	2,405	2,357
Current portion of long-term debt	2,099	699
Total current liabilities	4,504	3,058
Long-term debt, less current portion	78,460	81,661
Deferred income taxes	0	0
Other noncurrent liabilities	3,133	3,006
Redeemable noncontrolling interests	0	0
Equity:
Common stock	54	54
Other shareholders’ equity	74,905	71,559
Total Comcast Corporation shareholders’ equity	74,959	71,613
Noncontrolling interests	0	0
Total equity	74,959	71,613
Total liabilities and equity	161,056	159,338
Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Assets
Cash and cash equivalents	3,284	3,398
Receivables, net	10,736	11,104
Programming rights	2,942	3,746
Other current assets	2,974	3,070
Total current assets	19,936	21,318
Film and television costs	8,051	7,837
Investments	7,826	6,669
Investments in and amounts due from subsidiaries eliminated upon consolidation	98,613	97,872
Property and equipment, net	45,058	43,767
Franchise rights	59,365	59,365
Goodwill	68,073	66,154
Other intangible assets, net	36,892	38,347
Other noncurrent assets, net	7,642	4,910
Total assets	351,456	346,239
Liabilities and Equity
Accounts payable and accrued expenses related to trade creditors	10,232	8,492
Accrued participations and residuals	1,739	1,808
Deferred revenue	2,485	2,182
Accrued expenses and other current liabilities	5,595	7,572
Current portion of long-term debt	2,523	3,695
Total current liabilities	22,574	23,749
Long-term debt, less current portion	15,999	15,690
Deferred income taxes	27,980	27,734
Other noncurrent liabilities	14,033	11,056
Redeemable noncontrolling interests	1,316	1,316
Equity:
Common stock	0	0
Other shareholders’ equity	268,651	265,805
Total Comcast Corporation shareholders’ equity	268,651	265,805
Noncontrolling interests	903	889
Total equity	269,554	266,694
Total liabilities and equity	351,456	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	25	20
Total current assets	25	20
Film and television costs	0	0
Investments	11	11
Investments in and amounts due from subsidiaries eliminated upon consolidation	147,534	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	233	208
Total assets	147,803	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	149	150
Current portion of long-term debt	0	0
Total current liabilities	149	150
Long-term debt, less current portion	149	146
Deferred income taxes	324	314
Other noncurrent liabilities	0	0
Redeemable noncontrolling interests	0	0
Equity:
Common stock	0	0
Other shareholders’ equity	147,181	146,657
Total Comcast Corporation shareholders’ equity	147,181	146,657
Noncontrolling interests	0	0
Total equity	147,181	146,657
Total liabilities and equity	147,803	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	147	143
Investments in and amounts due from subsidiaries eliminated upon consolidation	129,829	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	129,976	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	245	360
Current portion of long-term debt	0	0
Total current liabilities	245	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	127,631	127,897
Total Comcast Corporation shareholders’ equity	127,631	127,897
Noncontrolling interests	0	0
Total equity	127,631	127,897
Total liabilities and equity	129,976	130,357
NBCUniversal Media Parent [Member] | Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Assets
Cash and cash equivalents	214	416
Receivables, net	0	0
Programming rights	0	0
Other current assets	26	28
Total current assets	240	444
Film and television costs	0	0
Investments	895	790
Investments in and amounts due from subsidiaries eliminated upon consolidation	56,005	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	93	85
Total assets	57,233	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	438	282
Current portion of long-term debt	7	4
Total current liabilities	445	286
Long-term debt, less current portion	7,756	7,748
Deferred income taxes	67	65
Other noncurrent liabilities	1,579	1,201
Redeemable noncontrolling interests	0	0
Equity:
Common stock	0	0
Other shareholders’ equity	47,386	45,872
Total Comcast Corporation shareholders’ equity	47,386	45,872
Noncontrolling interests	0	0
Total equity	47,386	45,872
Total liabilities and equity	$ 57,233	$ 55,172