Related Parties (Details)	Jun. 30, 2020 trustee
Related Party Transaction [Line Items]
SMR Trust ownership in NAI	80.00%
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