Stock-Based Compensation (Expense) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 04, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available for future grant under equity incentive plans (in shares)	33,000,000
RSUs and PSUs	$ 167	$ 169	$ 167
Stock options	19	27	34
Stock-based compensation	274	286	187
Related tax benefit	(54)	(58)	(44)
Stock-based compensation expense, net of tax benefit	220	228	143
Share-based compensation expense included in discontinued operations	10	5	4
SG&A Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	186	196	201
Restructuring Charges and Other Corporate Matters [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	$ 88	$ 90	$ (14)
Viacom Inc [Member] \| Common Class B [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share conversion ratio				0.59625

Amount, after tax, of expense for award under share-based payment arrangement.

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Amount of tax benefit for recognition of expense of award under share-based payment arrangement.

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Amount of noncash expense for award of restricted stock or unit under share-based payment arrangement.

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Amount of noncash expense for share-based payment arrangement.

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The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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Amount of noncash expense for option under share-based payment arrangement.

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Business Combination, Equity Interest Issued Or Issuable, Share Conversion Ratio

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Disposal Group, Including Discontinued Operation, Share-Based Compensation Expense

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