Pension and Other Postretirement Benefits (Plan Asset Allocations) (Details) - United States [Member]	Dec. 31, 2020
Fixed Income Instrument [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, actual plan asset allocation	73.00%
Equity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, actual plan asset allocation	25.00%
Viacom Inc [Member] \| Equity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, target plan asset allocations	78.00%
Viacom Inc [Member] \| Liability Hedging [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, target plan asset allocations	21.00%
Viacom Inc [Member] \| Cash and cash equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, target plan asset allocations	1.00%
Minimum [Member] \| Fixed Income Instrument [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, target plan asset allocations	70.00%
Minimum [Member] \| Equity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, target plan asset allocations	16.00%
Minimum [Member] \| Viacom Inc [Member] \| Equity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, target plan asset allocations	70.00%
Minimum [Member] \| Viacom Inc [Member] \| Liability Hedging [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, target plan asset allocations	10.00%
Minimum [Member] \| Viacom Inc [Member] \| Cash and cash equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, target plan asset allocations	0.00%
Maximum [Member] \| Fixed Income Instrument [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, target plan asset allocations	80.00%
Maximum [Member] \| Equity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, target plan asset allocations	28.00%
Maximum [Member] \| Viacom Inc [Member] \| Equity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, target plan asset allocations	90.00%
Maximum [Member] \| Viacom Inc [Member] \| Liability Hedging [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, target plan asset allocations	30.00%
Maximum [Member] \| Viacom Inc [Member] \| Cash and cash equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, target plan asset allocations	10.00%

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No definition available.

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- Definition

Percentage of target investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 55
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=118257860&loc=d3e4179-114921

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(i)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920

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- Definition

Percentage of actual investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(i)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920

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