Acquisitions and Dispositions - Pro Forma Combined Financial Information (Details) - First Data $ / shares in Units, $ in Millions	9 Months Ended
	Sep. 30, 2019 USD ($) $ / shares
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Total revenue	$ 11,730
Net income	463
Net income attributable to Fiserv, Inc.	$ 400
Net income per share attributable to Fiserv, Inc., Basic (in dollars per share) | $ / shares	$ 0.59
Net income per share attributable to Fiserv, Inc., Diluted (in dollars per share) | $ / shares	$ 0.58