Acquisitions and Dispositions - Pro Forma Combined Financial Information (Details) - First Data $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2021 USD ($) $ / shares
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Total revenue	$ 15,775
Net income	1,520
Net income attributable to Fiserv, Inc.	$ 1,457
Net income per share attributable to Fiserv, Inc.:
Net income per share attributable to Fiserv, Inc., Basic (in dollars per share) | $ / shares	$ 2.14
Net income per share attributable to Fiserv, Inc., Diluted (in dollars per share) | $ / shares	$ 2.10