v3.10.0.1
Document And Entity Information - USD ($)
12 Months Ended
Dec. 31, 2018
Feb. 25, 2019
Jun. 29, 2018
Document Information [Line Items]      
Document Type 10-K    
Amendment Flag false    
Document Period End Date Dec. 31, 2018    
Document Fiscal Year Focus 2018    
Document Fiscal Period Focus FY    
Trading Symbol ACIW    
Entity Registrant Name ACI WORLDWIDE, INC.    
Entity Central Index Key 0000935036    
Current Fiscal Year End Date --12-31    
Entity Well-known Seasoned Issuer No    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Filer Category Large Accelerated Filer    
Entity Common Stock, Shares Outstanding   116,143,338  
Entity Public Float     $ 2,181,473,639
Entity Small Business false    
Entity Emerging Growth Company false    
Entity Shell Company false