Recent Accounting Pronouncements (Policies)	3 Months Ended
Recent Accounting Pronouncements (Policies)	Mar. 31, 2019
Accounting Policies [Line Items]
Basis of Presentation	We have prepared these unaudited condensed consolidated financial statements based on SEC rules that permit reduced disclosure for interim periods. These financial statements include all adjustments that are necessary for a fair presentation of our consolidated results of operations, cash flows and financial condition for the periods shown, including normal, recurring accruals and other items. The consolidated results of operations for the interim periods presented are not necessarily indicative of results for the full year. The year-end condensed consolidated balance sheet was derived from audited financial statements but does not include all disclosures required by generally accepted accounting principles in the United States (“GAAP”). For a more complete discussion of our accounting policies and certain other information, refer to our consolidated financial statements included in our 2018 Annual Report on Form 10-K and the notes within this Form 10-Q.
Earnings Per Share	Diluted earnings per common share attributable to Comcast Corporation shareholders (“diluted EPS”) considers the impact of potentially dilutive securities using the treasury stock method. Our potentially dilutive securities include potential common shares related to our stock options and our restricted share units (“RSUs”). Diluted EPS excludes the impact of potential common shares related to our stock options in periods in which the combination of the option exercise price and the associated unrecognized compensation expense is greater than the average market price of our common stock.
Recent Accounting Pronouncements	In February 2016, the FASB updated the accounting guidance related to leases. The most significant change in the updated accounting guidance requires lessees to recognize lease assets and liabilities on the balance sheet for all operating leases with the exception of short-term leases. The standard also expands the disclosures regarding the amount, timing and uncertainty of cash flows arising from leases. For a lessee, the recognition, measurement and presentation of expenses and cash flows arising from a lease did not significantly change from previous guidance. We adopted the updated guidance on January 1, 2019 on a prospective basis and as a result, prior period amounts were not adjusted to reflect the impacts of the updated guidance. In addition, as permitted under the transition guidance within the new standard, prior scoping and classification conclusions were carried forward for leases existing as of the adoption date. Upon adoption, we recorded $4.2 billion and $4.8 billion for operating lease assets and liabilities, respectively, which includes the impact of fair value adjustments, prepaid and deferred rent and lease incentives. The adoption of the updated accounting guidance did not significantly impact our recognition of finance leases, which were previously described as capital leases. As of the date of adoption, our liabilities for finance leases were $787 million, including $229 million of additional contracts determined to be leases in connection with the Sky transaction, which were recorded in long-term debt, and the related assets were recorded in property and equipment, net. Our finance leases were not considered material for further disclosure. The adoption of the new accounting guidance did not have a material impact on our consolidated results of operations or cash flows. See Note 11 for further information. Film and Television Costs In March 2019, the FASB updated the accounting guidance related to film and television costs. The updated guidance aligns the accounting for production costs of episodic television series with those of films, allowing for costs to be capitalized in excess of amounts of revenue contracted for each episode. The updated guidance also updates certain presentation and disclosure requirements for capitalized film and television costs, and requires impairment testing to be performed at a group level for capitalized film and television costs when the content is predominately monetized with other owned or licensed content. The updated guidance is effective for us as of January 1, 2020 and early adoption is permitted. We are currently in the process of determining the impact that the updated accounting guidance will have on our consolidated financial statements, however we do not expect there to be a material impact on our consolidated results of operations or cash flows.
Leases	Our leases consist primarily of real estate, vehicles and other equipment. We determine if an arrangement is a lease at inception. Lease assets and liabilities are recognized upon commencement of the lease based on the present value of the future minimum lease payments over the lease term. The lease term includes options to extend the lease when it is reasonably certain that we will exercise that option. We generally utilize our incremental borrowing rate based on information available at the commencement of the lease in determining the present value of future payments. The lease asset also includes any lease payments made and initial direct costs incurred and excludes lease incentives. Lease assets and liabilities are not recorded for leases with an initial term of one year or less. Lease expense for operating leases recorded in the balance sheet is included in operating costs and expenses and is based on the future minimum lease payments recognized on a straight-line basis over the term of the lease plus any variable lease costs. Operating lease expenses, inclusive of short-term and variable lease expenses, recognized in our condensed consolidated statement of income for the three months ended March 31, 2019 were $274 million. These amounts do not include lease costs associated with production activities or other amounts capitalized in our condensed consolidated balance sheet, which are not material.
NBCUniversal Media LLC [Member]
Accounting Policies [Line Items]
Basis of Presentation	Unless indicated otherwise, throughout these notes to the condensed consolidated financial statements, we refer to NBCUniversal and its consolidated subsidiaries as “we,” “us” and “our.” We have prepared these unaudited condensed consolidated financial statements based on SEC rules that permit reduced disclosure for interim periods. These financial statements include all adjustments that are necessary for a fair presentation of our consolidated results of operations, cash flows and financial condition for the periods shown, including normal, recurring accruals and other items. The consolidated results of operations for the interim periods presented are not necessarily indicative of results for the full year. The year-end condensed consolidated balance sheet was derived from audited financial statements but does not include all disclosures required by generally accepted accounting principles in the United States (“GAAP”). For a more complete discussion of our accounting policies and certain other information, refer to our consolidated financial statements included in our 2018 Annual Report on Form 10-K and the notes within this Form 10-Q.
Recent Accounting Pronouncements	In February 2016, the FASB updated the accounting guidance related to leases. The most significant change in the updated accounting guidance requires lessees to recognize lease assets and liabilities on the balance sheet for all operating leases with the exception of short-term leases. The standard also expands the disclosures regarding the amount, timing and uncertainty of cash flows arising from leases. For a lessee, the recognition, measurement and presentation of expenses and cash flows arising from a lease did not significantly change from previous guidance. We adopted the updated guidance on January 1, 2019 on a prospective basis and as a result, prior period amounts were not adjusted to reflect the impacts of the updated guidance. In addition, as permitted under the transition guidance within the new standard, prior scoping and classification conclusions were carried forward for leases existing as of the adoption date. Upon adoption, we recorded approximately $1.7 billion and $1.8 billion of operating lease assets and liabilities, respectively, which includes the impact of fair value adjustments, prepaid rent and lease incentives. The adoption of the updated accounting guidance did not impact our recognition of finance leases, which were previously described as capital leases. As of the date of adoption, our liabilities for finance leases were $332 million, which were recorded in long-term debt, and the related assets were recorded in property and equipment, net. Our finance leases were not considered material for further disclosure. The adoption of the new accounting guidance did not have a material impact on our consolidated results of operations or cash flows. See Note 9 for further information. Film and Television Costs In March 2019, the FASB updated the accounting guidance related to film and television costs. The updated guidance aligns the accounting for production costs of episodic television series with those of films, allowing for costs to be capitalized in excess of amounts of revenue contracted for each episode. The updated guidance also updates certain presentation and disclosure requirements for capitalized film and television costs, and requires impairment testing to be performed at a group level for capitalized film and television costs when the content is predominately monetized with other owned or licensed content. The updated guidance is effective for us as of January 1, 2020 and early adoption is permitted. We are currently in the process of determining the impact that the updated accounting guidance will have on our consolidated financial statements, however we do not expect there to be a material impact on our consolidated results of operations or cash flows.
Leases	Our leases consist primarily of real estate and equipment. We determine if an arrangement is a lease at inception. Lease assets and liabilities are recognized upon commencement of the lease based on the present value of the future minimum lease payments over the lease term. The lease term includes options to extend the lease when it is reasonably certain that we will exercise that option. We generally utilize our incremental borrowing rate based on information available at the commencement of the lease in determining the present value of future payments. The lease asset also includes any lease payments made and initial direct costs incurred and excludes lease incentives. Lease assets and liabilities are not recorded for leases with an initial term of one year or less. Lease expense for operating leases recorded in the balance sheet is included in operating costs and expenses and is based on the future minimum lease payments recognized on a straight-line basis over the term of the lease plus any variable lease costs. Operating lease expenses, inclusive of short-term and variable lease expenses, recognized in our condensed consolidated statement of income for the three months ended March 31, 2019 were $111 million. These amounts do not include lease costs associated with production activities or other amounts capitalized in our condensed consolidated balance sheet, which are not material.