XML 12 R1.htm IDEA: XBRL DOCUMENT v3.19.1
Document and Entity Information - shares
shares in Millions
 3 Months Ended
Mar. 31, 2019
May 02, 2019
Entity Information [Line Items]    
Document Type 10-Q  
Entity Registrant Name ASGN Inc  
Trading Symbol ASGN  
Entity Listing, Description NYSE  
Entity Central Index Key 0000890564  
Current Fiscal Year End Date --12-31  
Entity Filer Category Large Accelerated Filer  
Document Period End Date Mar. 31, 2019  
Document Fiscal Year Focus 2019  
Document Fiscal Period Focus Q1  
Amendment Flag false  
Entity Small Business false  
Entity Emerging Growth Company false  
Entity Common Stock, Shares Outstanding   52.8