v3.8.0.1
Document and Entity Information - shares
3 Months Ended
Mar. 31, 2018
Apr. 30, 2018
Document Information [Line Items]    
Entity Registrant Name CBS Corporation  
Entity Central Index Key 0000813828  
Document Type 10-Q  
Document Period End Date Mar. 31, 2018  
Amendment Flag false  
Current Fiscal Year End Date --12-31  
Entity Filer Category Large Accelerated Filer  
Document Fiscal Year Focus 2018  
Document Fiscal Period Focus Q1  
Common Class A [Member]    
Document Information [Line Items]    
Shares of common stock outstanding   37,507,617
Common Class B [Member]    
Document Information [Line Items]    
Shares of common stock outstanding   341,480,807