Shares Used in Computing Net Income Per Share Attributable to Fiserv, Inc. - Schedule of Weighted-Average Number of Shares (Details) - shares shares in Millions |
3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
Jun. 30, 2026 |
Jun. 30, 2025 |
Jun. 30, 2026 |
Jun. 30, 2025 |
|
| Earnings Per Share [Abstract] | ||||
| Weighted-average common shares outstanding used for the calculation of net income attributable to Fiserv, Inc. per share – basic (in shares) | 532.6 | 550.8 | 533.4 | 556.1 |
| Common stock equivalents (in shares) | 1.1 | 1.9 | 1.1 | 2.6 |
| Weighted-average common shares outstanding used for the calculation of net income attributable to Fiserv, Inc. per share – diluted (in shares) | 533.7 | 552.7 | 534.5 | 558.7 |