Cover Page - shares	9 Months Ended
	Sep. 30, 2021	Oct. 22, 2021
Document Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2021
Document Transition Report	false
Entity File Number	1-38962
Entity Registrant Name	FISERV, INC.
Entity Incorporation, State or Country Code	WI
Entity Tax Identification Number	39-1506125
Entity Address, Address Line One	255 Fiserv Drive
Entity Address, City or Town	Brookfield,
Entity Address, State or Province	WI
Entity Address, Postal Zip Code	53045
City Area Code	262
Local Phone Number	879-5000
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		660,231,928
Amendment Flag	false
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q3
Entity Central Index Key	0000798354
Current Fiscal Year End Date	--12-31
Common Stock, par value $0.01 per share
Document Information [Line Items]
Title of 12(b) Security	Common Stock, par value $0.01 per share
Trading Symbol	FISV
Security Exchange Name	NASDAQ
0.375% Senior Notes due 2023
Document Information [Line Items]
Title of 12(b) Security	0.375% Senior Notes due 2023
Trading Symbol	FISV23
Security Exchange Name	NASDAQ
1.125% Senior Notes due 2027
Document Information [Line Items]
Title of 12(b) Security	1.125% Senior Notes due 2027
Trading Symbol	FISV27
Security Exchange Name	NASDAQ
1.625% Senior Notes due 2030
Document Information [Line Items]
Title of 12(b) Security	1.625% Senior Notes due 2030
Trading Symbol	FISV30
Security Exchange Name	NASDAQ
2.250% Senior Notes due 2025
Document Information [Line Items]
Title of 12(b) Security	2.250% Senior Notes due 2025
Trading Symbol	FISV25
Security Exchange Name	NASDAQ
3.000% Senior Notes due 2031
Document Information [Line Items]
Title of 12(b) Security	3.000% Senior Notes due 2031
Trading Symbol	FISV31
Security Exchange Name	NASDAQ