Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2019	Nov. 04, 2019
Entity Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 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		115,598,645
Amendment Flag	false
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q3
Entity Central Index Key	0000935036
Current Fiscal Year End Date	--12-31
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