Document and Entity Information - shares
6 Months Ended
Jun. 30, 2019
Aug. 05, 2019
Entity Information [Line Items]    
Document Type 10-Q  
Document Quarterly Report true  
Document Period End Date Jun. 30, 2019  
Document Transition Report false  
Entity File Number 0-25346  
Entity Registrant Name ACI WORLDWIDE, INC.  
Entity Incorporation, State or Country Code DE  
Entity Tax Identification Number 47-0772104  
Entity Address, Address Line One 3520 Kraft Rd,  
Entity Address, Address Line Two Suite 300  
Entity Address, City or Town Naples,  
Entity Address, State or Province FL  
Entity Address, Postal Zip Code 34105  
City Area Code 239  
Local Phone Number 403-4660  
Entity Current Reporting Status Yes  
Entity Interactive Data Current Yes  
Entity Filer Category Large Accelerated Filer  
Entity Small Business false  
Entity Emerging Growth Company false  
Entity Shell Company false  
Entity Common Stock, Shares Outstanding   116,714,472
Amendment Flag false  
Document Fiscal Year Focus 2019  
Document Fiscal Period Focus Q2  
Entity Central Index Key 0000935036  
Current Fiscal Year End Date --12-31  
Entity Information [Line Items]    
Title of 12(b) Security Common Stock, $0.005 par value  
Trading Symbol ACIW  
Security Exchange Name NASDAQ