Related Parties (Narrative) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($)	Dec. 31, 2020 trustee numberOfTrusts
Related Party Transaction [Line Items]
SMR trust ownership in NAI		80.00%
Number of continuing trusts | numberOfTrusts		2
Continuing trusts, voting stock ownership for each		40.00%
National Amusements Inc [Member]
Related Party Transaction [Line Items]
NAI ownership of CBS Corp. Class A common stock (percentage)		79.40%
NAI ownership of CBS Corp. Class A and Class B common stock on a combined basis (percentage)		10.20%
Number of trustees		7
Number of beneficiary trustees		2
National Amusements Inc [Member] | Restructuring Charges and Other Corporate Matters [Member]
Related Party Transaction [Line Items]
Professional fees | $	$ 30