| Document and Entity Information Document | Feb. 25, 2021 |
| Entity Information [Line Items] | |
| Document Type | 8-K |
| Document Period End Date | Feb. 25, 2021 |
| Entity File Number | 0-25346 |
| Entity Registrant Name | ACI WORLDWIDE, INC. |
| Entity Central Index Key | 0000935036 |
| Amendment Flag | false |
| 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 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| NASDAQ/NGS (GLOBAL SELECT MARKET) | |
| Entity Information [Line Items] | |
| Title of 12(b) Security | Common Stock, $0.005 par value |
| Trading Symbol | ACIW |
| Security Exchange Name | NASDAQ |
