| Document and Entity Information | Mar. 26, 2024 |
| Document And Entity Information [Line Items] | |
| Entity Registrant Name | FISERV INC |
| Amendment Flag | false |
| Entity Central Index Key | 0000798354 |
| Document Type | 8-K |
| Document Period End Date | Mar. 26, 2024 |
| Entity Incorporation State Country Code | WI |
| Entity File Number | 1-38962 |
| Entity Tax Identification Number | 39-1506125 |
| Entity Address, Address Line One | 600 N. Vel R. Phillips Avenue |
| Entity Address, City or Town | Milwaukee |
| Entity Address, State or Province | WI |
| Entity Address, Postal Zip Code | 53203 |
| City Area Code | (262) |
| Local Phone Number | 879-5000 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| Common Stock [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | Common Stock, par value $0.01 per share |
| Trading Symbol | FI |
| Security Exchange Name | NYSE |
| M 1.125 Senior Notes Due 20274 [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | 1.125% Senior Notes due 2027 |
| Trading Symbol | FI27 |
| Security Exchange Name | NYSE |
| M 1.625 Senior Notes Due 20301 [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | 1.625% Senior Notes due 2030 |
| Trading Symbol | FI30 |
| Security Exchange Name | NYSE |
| Senior Notes Due 2025 [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | 2.250% Senior Notes due 2025 |
| Trading Symbol | FI25 |
| Security Exchange Name | NYSE |
| M 3.000 Senior Notes Due 20312 [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | 3.000% Senior Notes due 2031 |
| Trading Symbol | FI31 |
| Security Exchange Name | NYSE |
| M 4.500 Senior Notes Due 20313 [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | 4.500% Senior Notes due 2031 |
| Trading Symbol | FI31A |
| Security Exchange Name | NYSE |
