v3.10.0.1
Condensed Consolidating Financial Information (Condensed Consolidating Statement of Income) (Details) - USD ($)
$ in Millions
 3 Months Ended 12 Months Ended
Dec. 31, 2018
Sep. 30, 2018
Jun. 30, 2018
Mar. 31, 2018
Dec. 31, 2017
Sep. 30, 2017
Jun. 30, 2017
Mar. 31, 2017
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Condensed Income Statements, Captions [Line Items]                      
Revenue $ 27,846 $ 22,135 $ 21,735 $ 22,791 $ 22,075 $ 21,081 $ 21,286 $ 20,587 $ 94,507 $ 85,029 $ 80,736
Costs and Expenses:                      
Programming and production                 29,692 25,355 24,348
Other operating and administrative                 28,094 25,449 23,840
Advertising, marketing and promotion                 7,036 6,519 6,291
Depreciation                 8,281 7,914 7,464
Amortization                 2,736 2,216 1,962
Other operating gains                 (341) (442) 0
Total costs and expenses                 75,498 67,011 63,905
Operating income 4,514 4,836 5,014 4,645 4,129 4,779 4,568 4,542 19,009 18,018 16,831
Interest expense                 (3,542) (3,086) (2,942)
Investment and other income (loss), net                 (225) 421 437
Income before income taxes                 15,242 15,353 14,326
Income tax (expense) benefit                 (3,380) 7,569 (5,298)
Net income                 11,862 22,922 9,028
Less: Net income attributable to noncontrolling interests and redeemable subsidiary preferred stock                 131 187 350
Net Income Attributable to Comcast Corporation $ 2,511 $ 2,886 $ 3,216 $ 3,118 $ 14,999 $ 2,642 $ 2,521 $ 2,573 11,731 22,735 8,678
Comprehensive income attributable to Comcast Corporation                 10,908 22,822 8,950
Elimination and Consolidation Adjustments [Member]                      
Condensed Income Statements, Captions [Line Items]                      
Revenue                 (2,372) (2,237) (2,116)
Costs and Expenses:                      
Programming and production                 0 0 0
Other operating and administrative                 (2,372) (2,237) (2,116)
Advertising, marketing and promotion                 0 0 0
Depreciation                 0 0 0
Amortization                 0 0 0
Other operating gains                 0 0 0
Total costs and expenses                 (2,372) (2,237) (2,116)
Operating income                 0 0 0
Interest expense                 0 0 0
Investment and other income (loss), net                 (51,236) (77,161) (37,441)
Income before income taxes                 (51,236) (77,161) (37,441)
Income tax (expense) benefit                 0 0 0
Net income                 (51,236) (77,161) (37,441)
Less: Net income attributable to noncontrolling interests and redeemable subsidiary preferred stock                 0 0 0
Net Income Attributable to Comcast Corporation                 (51,236) (77,161) (37,441)
Comprehensive income attributable to Comcast Corporation                 (50,328) (76,998) (37,656)
Comcast Parent [Member] | Reportable Legal Entities [Member]                      
Condensed Income Statements, Captions [Line Items]                      
Revenue                 1,197 1,128 1,067
Costs and Expenses:                      
Programming and production                 0 0 0
Other operating and administrative                 947 766 813
Advertising, marketing and promotion                 0 0 0
Depreciation                 46 31 28
Amortization                 5 6 6
Other operating gains                 0 0 0
Total costs and expenses                 998 803 847
Operating income                 199 325 220
Interest expense                 (2,644) (2,172) (1,941)
Investment and other income (loss), net                 13,638 24,076 9,799
Income before income taxes                 11,193 22,229 8,078
Income tax (expense) benefit                 538 506 600
Net income                 11,731 22,735 8,678
Less: Net income attributable to noncontrolling interests and redeemable subsidiary preferred stock                 0 0 0
Net Income Attributable to Comcast Corporation                 11,731 22,735 8,678
Comprehensive income attributable to Comcast Corporation                 10,908 22,822 8,950
Subsidiary Issuer [Member] | Reportable Legal Entities [Member] | Comcast Holdings [Member]                      
Condensed Income Statements, Captions [Line Items]                      
Revenue                 0 0 0
Costs and Expenses:                      
Programming and production                 0 0 0
Other operating and administrative                 0 0 0
Advertising, marketing and promotion                 0 0 0
Depreciation                 0 0 0
Amortization                 0 0 0
Other operating gains                 0 0 0
Total costs and expenses                 0 0 0
Operating income                 0 0 0
Interest expense                 (12) (12) (12)
Investment and other income (loss), net                 13,604 21,767 9,289
Income before income taxes                 13,592 21,755 9,277
Income tax (expense) benefit                 8 156 6
Net income                 13,600 21,911 9,283
Less: Net income attributable to noncontrolling interests and redeemable subsidiary preferred stock                 0 0 0
Net Income Attributable to Comcast Corporation                 13,600 21,911 9,283
Comprehensive income attributable to Comcast Corporation                 13,623 21,909 9,325
Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member] | CCCL Parent [Member]                      
Condensed Income Statements, Captions [Line Items]                      
Revenue                 1,175 1,109 1,049
Costs and Expenses:                      
Programming and production                 0 0 0
Other operating and administrative                 1,175 1,109 1,049
Advertising, marketing and promotion                 0 0 0
Depreciation                 0 0 0
Amortization                 0 0 0
Other operating gains                 0 0 0
Total costs and expenses                 1,175 1,109 1,049
Operating income                 0 0 0
Interest expense                 (190) (207) (239)
Investment and other income (loss), net                 12,021 19,610 8,703
Income before income taxes                 11,831 19,403 8,464
Income tax (expense) benefit                 40 71 84
Net income                 11,871 19,474 8,548
Less: Net income attributable to noncontrolling interests and redeemable subsidiary preferred stock                 0 0 0
Net Income Attributable to Comcast Corporation                 11,871 19,474 8,548
Comprehensive income attributable to Comcast Corporation                 11,873 19,477 8,554
Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member] | NBCUniversal Media Parent [Member]                      
Condensed Income Statements, Captions [Line Items]                      
Revenue                 0 0 0
Costs and Expenses:                      
Programming and production                 0 0 0
Other operating and administrative                 1,023 1,044 932
Advertising, marketing and promotion                 0 0 0
Depreciation                 0 0 0
Amortization                 0 0 0
Other operating gains                 0 0 0
Total costs and expenses                 1,023 1,044 932
Operating income                 (1,023) (1,044) (932)
Interest expense                 (430) (456) (456)
Investment and other income (loss), net                 6,694 6,584 5,572
Income before income taxes                 5,241 5,084 4,184
Income tax (expense) benefit                 (4) (4) (13)
Net income                 5,237 5,080 4,171
Less: Net income attributable to noncontrolling interests and redeemable subsidiary preferred stock                 0 0 0
Net Income Attributable to Comcast Corporation                 5,237 5,080 4,171
Comprehensive income attributable to Comcast Corporation                 5,279 5,054 4,248
Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]                      
Condensed Income Statements, Captions [Line Items]                      
Revenue                 94,507 85,029 80,736
Costs and Expenses:                      
Programming and production                 29,692 25,355 24,348
Other operating and administrative                 27,321 24,767 23,162
Advertising, marketing and promotion                 7,036 6,519 6,291
Depreciation                 8,235 7,883 7,436
Amortization                 2,731 2,210 1,956
Other operating gains                 (341) (442) 0
Total costs and expenses                 74,674 66,292 63,193
Operating income                 19,833 18,737 17,543
Interest expense                 (266) (239) (294)
Investment and other income (loss), net                 5,054 5,545 4,515
Income before income taxes                 24,621 24,043 21,764
Income tax (expense) benefit                 (3,962) 6,840 (5,975)
Net income                 20,659 30,883 15,789
Less: Net income attributable to noncontrolling interests and redeemable subsidiary preferred stock                 131 187 350
Net Income Attributable to Comcast Corporation                 20,528 30,696 15,439
Comprehensive income attributable to Comcast Corporation                 19,553 30,558 15,529
Service [Member]                      
Condensed Income Statements, Captions [Line Items]                      
Revenue                 94,507 85,029 80,736
Service [Member] | Elimination and Consolidation Adjustments [Member]                      
Condensed Income Statements, Captions [Line Items]                      
Revenue                 0 0 0
Service [Member] | Comcast Parent [Member] | Reportable Legal Entities [Member]                      
Condensed Income Statements, Captions [Line Items]                      
Revenue                 0 0 0
Service [Member] | Subsidiary Issuer [Member] | Reportable Legal Entities [Member] | Comcast Holdings [Member]                      
Condensed Income Statements, Captions [Line Items]                      
Revenue                 0 0 0
Service [Member] | Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member] | CCCL Parent [Member]                      
Condensed Income Statements, Captions [Line Items]                      
Revenue                 0 0 0
Service [Member] | Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member] | NBCUniversal Media Parent [Member]                      
Condensed Income Statements, Captions [Line Items]                      
Revenue                 0 0 0
Service [Member] | Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]                      
Condensed Income Statements, Captions [Line Items]                      
Revenue                 94,507 85,029 80,736
Management Fee [Member]                      
Condensed Income Statements, Captions [Line Items]                      
Revenue                 0 0 0
Management Fee [Member] | Elimination and Consolidation Adjustments [Member]                      
Condensed Income Statements, Captions [Line Items]                      
Revenue                 (2,372) (2,237) (2,116)
Management Fee [Member] | Comcast Parent [Member] | Reportable Legal Entities [Member]                      
Condensed Income Statements, Captions [Line Items]                      
Revenue                 1,197 1,128 1,067
Management Fee [Member] | Subsidiary Issuer [Member] | Reportable Legal Entities [Member] | Comcast Holdings [Member]                      
Condensed Income Statements, Captions [Line Items]                      
Revenue                 0 0 0
Management Fee [Member] | Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member] | CCCL Parent [Member]                      
Condensed Income Statements, Captions [Line Items]                      
Revenue                 1,175 1,109 1,049
Management Fee [Member] | Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member] | NBCUniversal Media Parent [Member]                      
Condensed Income Statements, Captions [Line Items]                      
Revenue                 0 0 0
Management Fee [Member] | Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]                      
Condensed Income Statements, Captions [Line Items]                      
Revenue                 $ 0 $ 0 $ 0