Acquisitions and Dispositions - Pro Forma Combined Financial Information (Details) - First Data - USD ($) $ / shares in Units, $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Total revenue	$ 3,988	$ 7,796
Net income	303	285
Net income attributable to Fiserv, Inc.	$ 275	$ 233
Net income per share attributable to Fiserv, Inc., Basic (in dollars per share)	$ 0.41	$ 0.34
Net income per share attributable to Fiserv, Inc., Diluted (in dollars per share)	$ 0.40	$ 0.34