Cover Page - USD ($)	12 Months Ended
	Dec. 31, 2021	Feb. 18, 2022	Jun. 30, 2021
Document Information [Line Items]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2021
Current Fiscal Year End Date	--12-31
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 Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
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
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float			$ 70,526,209,592
Entity Common Stock, Shares Outstanding		652,196,905
Documents Incorporated by Reference	Part III of this report incorporates information by reference to the registrant’s proxy statement for its 2022 annual meeting of shareholders, which proxy statement will be filed with the Securities and Exchange Commission no later than 120 days after the close of the fiscal year ended December 31, 2021.
Entity Central Index Key	0000798354
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	FY
Amendment Flag	false
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