Document and Entity Information
| Document and Entity Information | May 19, 2021 |
| 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 | May 19, 2021 |
| Entity Incorporation State Country Code | WI |
| Entity File Number | 1-38962 |
| 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 |
| 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 | FISV |
| Security Exchange Name | NASDAQ |
| Senior Notes Due 2023 [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | 0.375% Senior Notes due 2023 |
| Trading Symbol | FISV23 |
| Security Exchange Name | NASDAQ |
| Senior Notes Due 2027 [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | 1.125% Senior Notes due 2027 |
| Trading Symbol | FISV27 |
| Security Exchange Name | NASDAQ |
| Senior Notes Due 2030 [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | 1.625% Senior Notes due 2030 |
| Trading Symbol | FISV30 |
| Security Exchange Name | NASDAQ |
| Senior Notes Due 2025 [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | 2.250% Senior Notes due 2025 |
| Trading Symbol | FISV25 |
| Security Exchange Name | NASDAQ |
| Senior Notes Due 2031 [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | 3.000% Senior Notes due 2031 |
| Trading Symbol | FISV31 |
| Security Exchange Name | NASDAQ |