| Summary of Significant Accounting Policies (Policies) | 12 Months Ended |
| Sep. 30, 2017 |
| Accounting Policies [Abstract] | |
| Principles of Consolidation | Principles of Consolidation Our consolidated financial statements include the accounts of Viacom Inc., its subsidiaries and variable interest entities (“VIEs”) where we are considered the primary beneficiary, after elimination of intercompany accounts and transactions. Investments in business entities in which Viacom lacks control but does have the ability to exercise significant influence over operating and financial policies are accounted for using the equity method. Our proportionate share of net income or loss of the entity is recorded in Equity in net earnings of investee companies in the Consolidated Statements of Earnings. |
| Business Combinations | Business Combinations We account for business combinations using the acquisition method of accounting. Under the acquisition method, once control is obtained of a business, 100% of the assets, liabilities and certain contingent liabilities acquired, including amounts attributed to noncontrolling interests, are recorded at fair value. Any transaction costs are expensed as incurred. |
| Foreign Currency Translation and Remeasurement | Foreign Currency Translation and Remeasurement Assets and liabilities of subsidiaries with a functional currency other than the United States (“U.S.”) Dollar are translated into U.S. Dollars using period-end exchange rates, while results of operations are translated at exchange rates during the period. Foreign currency translation gains and losses are included as a component of Accumulated other comprehensive loss in the Consolidated Balance Sheets. Substantially all of our foreign operations use the local currency as the functional currency. Subsidiaries that enter into transactions denominated in currencies other than their functional currency will result in remeasurement gains and losses which are reflected within Other items, net in the Consolidated Statements of Earnings. |
| Revenue Recognition | Revenue Recognition We recognize revenue when it is realized or realizable and earned. We consider revenue realized or realizable and earned when there is persuasive evidence of an arrangement, delivery has occurred, the sales price is fixed or determinable, and collectability is reasonably assured. Determining whether some or all of these criteria have been met involves assumptions and judgments that can have a significant impact on the timing and amount of revenue we report. This includes the evaluation of multiple element arrangements for bundled advertising sales and content licenses, which involves allocating the consideration among individual deliverables within the bundled arrangement. Advertising Revenues : Revenue from the sale of advertising earned by the Media Networks segment is recognized, net of agency commissions, when the advertisement is aired and the contracted audience rating is met. For advertising sold based on impression guarantees, audience deficiency may result in an obligation to deliver subsequent additional units. To the extent we do not satisfy contracted audience ratings, we record deferred revenue until such time that the impression guarantee has been satisfied. Film and Television Production Revenues : Theatrical revenue is recognized from theatrical distribution of motion pictures upon exhibition. For sales of DVDs and Blue-ray discs to wholesalers and retailers, revenue is recognized upon the later of delivery or the date that those products are made widely available for sale by retailers. Revenue for transactional video-on-demand and similar arrangements are recognized as the films are exhibited based on end-customer purchases as reported by the distributor. Revenue from the licensing of film and television exhibition rights is recognized upon availability for airing by the licensee. Affiliate Revenues : Affiliate revenues from cable television operators, direct-to-home satellite television operators and mobile networks are recognized by the Media Networks segment as the service is provided to the distributor. Fees associated with arrangements with subscription video-on-demand and other over-the-top (“OTT”) services are recognized upon program availability. Ancillary Revenues : Revenue associated with consumer products and brand licensing is typically recognized utilizing contractual royalty rates applied to sales amounts reported by licensees. Revenue from licensing of our programming content for download-to-own and download-to-rent services is recognized when we are notified by the multi-platform retailer that the product has been downloaded and all other revenue recognition criteria are met. Multiple-Element Arrangements : We enter into arrangements under which we perform multiple revenue-generating activities. We allocate consideration to separate units of account in the arrangement and recognize the associated revenue as each unit of account is delivered. Advertising revenues are principally generated from the sale of advertising time comprised of multiple commercial units. Each advertising spot comprises a deliverable for accounting purposes. Consideration for these arrangements is allocated among the individual advertising spots based on relative fair value using Viacom-specific prices. Subscription video-on-demand and other OTT arrangements include certain programs made available to distributors on one or more dates for a fixed fee. Consideration for such arrangements is allocated among the programs based on relative fair value using management’s best estimate considering viewing performance and other factors. Gross versus Net Revenue : We earn and recognize revenues as a distributor on behalf of third parties and through outsourced agency agreements. In such cases, determining whether revenue should be reported on a gross or net basis is based on management’s assessment of who our customer is in the transaction. To the extent the end consumer is our customer, we act as the principal in a transaction and revenues earned from the end user are reported on a gross basis. This determination involves judgment and is based on an evaluation of whether we have the substantial risks and rewards under the terms of an arrangement. |
| Revenue Allowances | Revenue Allowances : We record a provision for sales returns and allowances at the time of sale based upon an estimate of future returns, rebates and other incentives (“estimated returns”). In determining estimated returns, we consider numerous sources of qualitative and quantitative evidence including forecasted sales data, customers’ rights of return, units shipped and units remaining at retail, historical return rates for similar product, current economic trends, competitive environment, promotions and sales strategies. Reserves for accounts receivable are based on amounts estimated to be uncollectible. Our reserve for sales returns and allowances was $79 million and $93 million at September 30, 2017 and 2016 , respectively. Our allowance for doubtful accounts was $49 million and $44 million at September 30, 2017 and 2016 , respectively. |
| Advertising Expense | Advertising Expense We expense advertising costs as they are incurred. We incurred total advertising expenses of $1.335 billion in 2017 , $987 million in 2016 and $748 million in 2015 . |
| Equity-Based Compensation | Equity-Based Compensation We measure the cost of employee services received in exchange for an award of equity instruments based on the grant date fair value of the award. The fair value received is recognized in earnings over the period during which an employee is required to provide service. |
| Income Taxes | Income Taxes Our provision for income taxes includes the current tax owed on the current period earnings, as well as a deferred provision which reflects the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective income tax bases. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. Changes in existing tax laws and rates, their related interpretations, as well as the uncertainty generated by the prospect of tax legislation in the future may affect the amounts of deferred tax liabilities or the realizability of deferred tax assets. Deferred tax assets and deferred tax liabilities are classified as noncurrent and are included in Other Assets and Deferred tax liabilities, net , respectively, within the Consolidated Balance Sheets. For tax positions we have taken or expect to take in a tax return, we apply a more likely than not assessment (i.e., there is a greater than 50 percent chance) about whether the tax position will be sustained upon examination by the appropriate tax authority with full knowledge of all relevant information. Amounts recorded for uncertain tax positions are periodically assessed, including the evaluation of new facts and circumstances, to ensure sustainability of the position. Interest and penalties related to uncertain tax positions are included in the Provision for income taxes in the Consolidated Statements of Earnings . Liabilities for uncertain tax positions are classified as Other liabilities – noncurrent in the Consolidated Balance Sheets. |
| Earnings Per Common Share | Earnings per Common Share Basic earnings per common share is computed by dividing Net earnings attributable to Viacom by the weighted average number of common shares outstanding during the period. The determination of diluted earnings per common share includes the weighted average number of common shares plus the dilutive effect of equity awards based upon the application of the treasury stock method. Anti-dilutive common shares are excluded from the calculation of diluted earnings per common share. |
| Comprehensive Income | Comprehensive Income Comprehensive income includes net earnings, foreign currency translation adjustments, amortization of amounts related to defined benefit plans, unrealized gains and losses on certain derivative financial instruments, and unrealized gains and losses on investments in equity securities which are publicly traded. |
| Cash and Cash Equivalents | Cash and Cash Equivalents All highly liquid investments with maturities of three months or less at the date of purchase are considered to be cash equivalents. |
| Inventory | Inventory Inventories related to film and television productions (which include direct production costs, production overhead, acquisition costs and development costs) are stated at the lower of amortized cost or fair value. Acquired program rights and obligations are recorded based on the gross amount of the liability when the license period has begun, and when the program is accepted and available for airing. Acquired programming is stated at the lower of unamortized cost or net realizable value. Film, television and acquired programming inventories are included as a component of Inventory, net , in the Consolidated Balance Sheets. Film, television and acquired programming costs, including inventory amortization, development costs, residuals and participations and impairment charges, if any, are included within Operating expenses in the Consolidated Statements of Earnings. Film and television production costs : We use an individual-film-forecast-computation method to amortize film costs and to accrue estimated liabilities for residuals and participations over the applicable title’s life cycle based upon the ratio of current period to estimated remaining total gross revenues (“ultimate revenues”) for each title. The estimate of ultimate revenues impacts the timing of amortization and accrual of residuals and participations. Our estimate of ultimate revenues for feature films includes revenues from all sources that are estimated to be earned within 10 years from the date of a film’s initial theatrical release. For acquired film libraries, our estimate of ultimate revenues is for a period within 20 years from the date of acquisition. These estimates are periodically reviewed and adjustments, if any, will result in changes to inventory amortization rates, estimated accruals for residuals and participations or possibly the recognition of an impairment charge to operating income. Film development costs that have not been set for production are expensed within three years unless they are abandoned earlier, in which case these projects are written down to their estimated fair value in the period the decision to abandon the project is determined. We have a rigorous greenlight process designed to manage the risk of loss or abandonment. Capitalized original programming costs are amortized utilizing an individual-film-forecast-computation method over the applicable title’s ultimate revenues based on genre and historical experience, beginning with the month of initial exhibition. Original programming costs that have not been greenlit for production are expensed. An impairment charge is recorded when the fair value of the television program is less than the unamortized production cost or abandoned. Acquired programming : Costs incurred in acquiring program rights, including advances, are capitalized and amortized over the license period or projected useful life of the programming, if shorter, commencing upon availability, based on estimated future airings. If initial airings are expected to generate higher revenues an accelerated method of amortization is used. Net realizable value of acquired rights programming is evaluated quarterly by us on a daypart basis, which is defined as an aggregation of programs broadcast during a particular time of day or an aggregation of programs of a similar type. We aggregate similar programming based on the specific demographic targeted by each respective program service. Net realizable value is determined by estimating advertising revenues to be derived from the future airing of the programming within the daypart as well as an allocation of affiliate revenue to the programming. An impairment charge may be necessary if our estimates of future cash flows of similar programming are insufficient or if programming is abandoned. Home entertainment inventory : Home entertainment inventory is valued at the lower of cost or net realizable value. Cost is determined using the average cost method. |
| Property and Equipment | Property and Equipment Property and equipment is stated at cost. Depreciation is calculated using the straight-line method. Leasehold improvements are amortized using the straight-line method over the shorter of their useful lives or the life of the lease. Costs associated with repairs and maintenance of property and equipment are expensed as incurred. |
| Goodwill, Intangible Assets and Other Long-Lived Assets | Goodwill, Intangible Assets and Other Long-Lived Assets Goodwill represents the residual difference between the consideration paid for a business and the fair value of the net assets acquired. Goodwill is not amortized, but rather is tested annually for impairment, on August 31 each year, or sooner when circumstances indicate impairment may exist. Goodwill is tested for impairment at the reporting unit level, which is an operating segment, or a business which is one level below that operating segment. Identifiable intangible assets with finite lives are amortized over their estimated useful lives, which range up to 20 years, and identifiable intangible assets with indefinite lives are not amortized, but rather are tested annually for impairment, or sooner when circumstances indicate impairment may exist. Amortizable intangible assets and other long-lived assets are tested for impairment utilizing an income approach based on undiscounted cash flows upon the occurrence of certain triggering events and, if impaired, are written down to fair value. The impairment test is performed at the lowest level of cash flows associated with the asset. |
| Investments | Investments Our investments primarily consist of investments in equity. Investments in which we have a significant influence, but not a controlling interest, are accounted for using the equity method. Other investments are carried at fair value, to the extent publicly traded, with unrealized gains and losses recorded in other comprehensive income, or at cost. We monitor our investments for impairment at least annually and make appropriate reductions in carrying values if we determine that an impairment charge is required based on qualitative and quantitative information. Our investments are included in Other assets – noncurrent in the Consolidated Balance Sheets. |
| Guarantees | Guarantees At the inception of a guarantee, we recognize a liability for the fair value of an obligation assumed by issuing the guarantee. The related liability is subsequently reduced as utilized or extinguished and increased if there is a probable loss associated with the guarantee which exceeds the value of the recorded liability. |
| Treasury Stock | Treasury Stock Treasury stock is accounted for using the cost method. |
| Fair Value Measurements | Fair Value Measurements Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. The framework for measuring fair value provides a hierarchy that prioritizes the inputs to valuation techniques used in measuring fair value. The hierarchy gives the highest priority to unadjusted quoted prices in active markets for identical assets or liabilities (Level 1 measurement) and the lowest priority to unobservable inputs (Level 3 measurement). The three levels of the fair value hierarchy are as follows: • Level 1 – Inputs to the valuation methodology are unadjusted quoted prices for identical assets or liabilities in active markets. • Level 2 – Inputs to the valuation methodology include: quoted prices for similar assets or liabilities in active markets; quoted prices for identical or similar assets or liabilities in inactive markets; inputs other than quoted prices that are observable for the asset or liability; inputs that are derived principally from or corroborated by observable market data by correlation or other means. • Level 3 – Inputs to the valuation methodology are unobservable and significant to the fair value measurement. |
| Derivative Financial Instruments | Derivative Financial Instruments Derivative financial instruments are recorded on the Consolidated Balance Sheets as assets or liabilities and measured at fair value. For derivatives designated as hedges of the fair value of assets or liabilities, the changes in fair value of both the derivatives and the hedged items are recorded in current earnings as part of Other items, net in the Consolidated Statements of Earnings. For derivatives designated as cash flow hedges, the effective portion of the changes in fair value of the derivatives is recorded in Accumulated other comprehensive loss in the Consolidated Balance Sheets and subsequently recognized in earnings when the hedged items impact income. The fair value of derivative financial instruments is included in Prepaid and other assets and Other liabilities – current in the Consolidated Balance Sheets. Changes in the fair value of derivatives not designated as hedges and the ineffective portion of cash flow hedges are recorded in earnings. We do not hold or enter into financial instruments for speculative trading purposes. |
| Pension Benefits | Pension Benefits Our defined benefit pension plans principally consist of both funded and unfunded noncontributory plans covering the majority of domestic employees and retirees. The funded defined benefit pension plan and unfunded pension plans are currently frozen to future benefit accruals. The expense we recognize is determined using certain assumptions, including the expected long-term rate of return and discount rate, among others. We recognize the funded status of our defined benefit plans (other than a multiemployer plan) as an asset or liability in the Consolidated Balance Sheets and recognize the changes in the funded status in the year in which the changes occur through Accumulated other comprehensive loss in the Consolidated Balance Sheets. |
| Collaborative Arrangements | Our collaborative arrangements principally relate to contractual arrangements with other studios to jointly finance and distribute theatrical productions (“co-financing arrangements”). A co-financing arrangement typically involves joint ownership of the film asset with each partner responsible for distribution of the film in specific territories. The partners share in the profits and losses of the film in accordance with their respective ownership interest. The amounts recorded in the Consolidated Statements of Earnings related to collaborative arrangements were not material . |
