v3.26.1
Debt - Narrative (Details)
€ in Millions, $ in Millions
3 Months Ended 6 Months Ended
Jul. 01, 2026
USD ($)
Jun. 23, 2026
USD ($)
Jun. 30, 2026
USD ($)
Jun. 30, 2025
USD ($)
Jun. 30, 2026
USD ($)
Jun. 30, 2025
USD ($)
Jun. 23, 2026
EUR (€)
Dec. 31, 2025
USD ($)
Aug. 12, 2025
USD ($)
Aug. 11, 2025
USD ($)
Jul. 31, 2025
May 07, 2025
EUR (€)
Debt Instrument [Line Items]                        
Repayments of senior debt   $ 1,200                    
Gain on early debt extinguishment     $ 154 $ 0 $ 154 $ 0            
Foreign lines of credit                        
Debt Instrument [Line Items]                        
Weighted-Average Interest Rate     17.401%   17.401%     27.727%        
Senior Notes                        
Debt Instrument [Line Items]                        
Debt instrument, face amount             € 1,000     $ 2,000    
Debt instrument, interest rate, increase (decrease) due to credit rating below investment grade         2.00%              
Senior Notes | Fiserv Funding Unlimited Company                        
Debt Instrument [Line Items]                        
Debt instrument, face amount | €                       € 2,175
Senior Notes | 3.750% senior notes due October 2030 (Euro-denominated)                        
Debt Instrument [Line Items]                        
Debt instrument, face amount | €             € 500          
Debt instrument, interest rate   3.75% 3.75%   3.75%   3.75%          
Outstanding borrowings     $ 569   $ 569     $ 0        
Senior Notes | 4.250% senior notes due June 2034 (Euro-denominated)                        
Debt Instrument [Line Items]                        
Debt instrument, face amount | €             € 500          
Debt instrument, interest rate   4.25% 4.25%   4.25%   4.25%          
Outstanding borrowings     $ 569   $ 569     0        
Senior Notes | 5.150% senior notes due March 2027                        
Debt Instrument [Line Items]                        
Debt instrument, interest rate   5.15% 5.15%   5.15%   5.15%          
Outstanding borrowings     $ 234   $ 234     750        
Senior Notes | 4.400% senior notes due July 2049                        
Debt Instrument [Line Items]                        
Debt instrument, face amount     $ 28   $ 28              
Debt instrument, interest rate   4.40% 4.40%   4.40%   4.40%          
Repayments of senior debt     $ 23                  
Outstanding borrowings     $ 1,156   $ 1,156     2,000        
Senior Notes | 4.400% senior notes due July 2049 | Subsequent Event                        
Debt Instrument [Line Items]                        
Debt instrument, face amount $ 47                      
Repayments of senior debt $ 38                      
Senior Notes | 5.150% Senior Notes Due March 2027 and 4.400% Senior Notes Due July 2049                        
Debt Instrument [Line Items]                        
Debt instrument, face amount   $ 1,300                    
Senior Notes | 4.550% senior notes due February 2031                        
Debt Instrument [Line Items]                        
Debt instrument, face amount                   $ 1,000    
Debt instrument, interest rate     4.55%   4.55%         4.55%    
Outstanding borrowings     $ 1,000   $ 1,000     1,000        
Senior Notes | 5.250% senior notes due August 2035                        
Debt Instrument [Line Items]                        
Debt instrument, face amount                   $ 1,000    
Debt instrument, interest rate     5.25%   5.25%         5.25%    
Outstanding borrowings     $ 1,000   $ 1,000     1,000        
Senior Notes | 2.875% senior notes due June 2028 (Euro-denominated)                        
Debt Instrument [Line Items]                        
Outstanding borrowings     $ 854   $ 854     883        
Senior Notes | 2.875% senior notes due June 2028 (Euro-denominated) | Fiserv Funding Unlimited Company                        
Debt Instrument [Line Items]                        
Debt instrument, face amount | €                       € 750
Debt instrument, interest rate     2.875%   2.875%             2.875%
Senior Notes | 3.500% senior notes due June 2032 (Euro-denominated)                        
Debt Instrument [Line Items]                        
Outstanding borrowings     $ 882   $ 882     912        
Senior Notes | 3.500% senior notes due June 2032 (Euro-denominated) | Fiserv Funding Unlimited Company                        
Debt Instrument [Line Items]                        
Debt instrument, face amount | €                       € 775
Debt instrument, interest rate     3.50%   3.50%             3.50%
Senior Notes | 4.0% Senior Notes Due June 2036                        
Debt Instrument [Line Items]                        
Outstanding borrowings     $ 740   $ 740     765        
Senior Notes | 4.0% Senior Notes Due June 2036 | Fiserv Funding Unlimited Company                        
Debt Instrument [Line Items]                        
Debt instrument, face amount | €                       € 650
Debt instrument, interest rate     4.00%   4.00%             4.00%
Senior Notes | 3.85% Senior Notes Due June 2025                        
Debt Instrument [Line Items]                        
Debt instrument, interest rate                       3.85%
Senior Notes | 2.25% Senior Notes Due July 2025                        
Debt Instrument [Line Items]                        
Debt instrument, interest rate                     2.25% 2.25%
Senior Notes | 4.750% senior notes due March 2030                        
Debt Instrument [Line Items]                        
Debt instrument, interest rate     4.75%   4.75%              
Outstanding borrowings     $ 850   $ 850     850        
Senior Notes | 5.150% senior notes due August 2034                        
Debt Instrument [Line Items]                        
Debt instrument, interest rate     5.15%   5.15%              
Outstanding borrowings     $ 900   $ 900     900        
Senior Notes | 5.350% senior notes due March 2031                        
Debt Instrument [Line Items]                        
Debt instrument, interest rate     5.35%   5.35%              
Outstanding borrowings     $ 500   $ 500     500        
Senior Notes | 5.450% senior notes due March 2034                        
Debt Instrument [Line Items]                        
Debt instrument, interest rate     5.45%   5.45%              
Outstanding borrowings     $ 750   $ 750     750        
Senior Notes | 3.200% senior notes due July 2026                        
Debt Instrument [Line Items]                        
Debt instrument, interest rate     3.20%   3.20%              
Outstanding borrowings     $ 2,000   $ 2,000     2,000        
Commercial Paper | U.S. dollar commercial paper notes                        
Debt Instrument [Line Items]                        
Debt maturities (in days)         397 days              
Outstanding borrowings     0   $ 0     $ 326        
Weighted-Average Interest Rate               3.851%        
Commercial Paper | Euro commercial paper notes                        
Debt Instrument [Line Items]                        
Debt maturities (in days)         183 days              
Outstanding borrowings     $ 548   $ 548     $ 839        
Weighted-Average Interest Rate     2.493%   2.493%     2.21%        
Revolving credit facility | Line of Credit                        
Debt Instrument [Line Items]                        
Outstanding borrowings     $ 0   $ 0     $ 188        
Weighted-Average Interest Rate               4.685%        
Maximum borrowing capacity                 $ 8,000      
Outstanding borrowings     $ 0   $ 0     $ 188        
Debt instrument, covenant, debt-to-EBITDA ratio     3.75   3.75