Related Party Transactions	9 Months Ended
Related Party Transactions	Sep. 30, 2021
Related Party Transactions [Abstract]
Related Party Transactions	Related Party Transactions Merchant Alliances The Company maintains ownership interests of significant influence in various merchant alliances and strategic investments in companies in related markets. A merchant alliance is an agreement between the Company and a financial institution that combines the processing capabilities and management expertise of the Company with the visibility and distribution channel of the financial institution. A merchant alliance acquires credit and debit card transactions from merchants. The Company provides processing and other services to the alliance and charges fees to the alliance primarily based on contractual pricing. A significant portion of the Company’s business is conducted through merchant alliances between the Company and financial institutions. To the extent the Company maintains a controlling financial interest in an alliance, the alliance’s financial statements are consolidated with those of the Company and the related processing fees are treated as an intercompany transaction and eliminated in consolidation. To the extent the Company has significant influence but not control in an alliance, the Company uses the equity method of accounting to account for its investment in the alliance. As a result, the processing and other service fees charged to merchant alliances accounted for under the equity method are recognized in the Company’s consolidated statements of income primarily as processing and services revenue. Such fees totaled $42 million and $47 million for the three months ended September 30, 2021 and 2020, respectively, and $132 million and $134 million for the nine months ended September 30, 2021 and 2020, respectively. No directors or officers of the Company have ownership interests in any of the alliances. The formation of each of these alliances generally involves the Company and the financial institution contributing contractual merchant relationships to the alliance and a cash payment from one owner to the other to achieve the desired ownership percentage for each. The Company and the financial institution enter into a long-term processing service agreement as part of the negotiation process. This agreement governs the Company’s provision of transaction processing services to the alliance. The Company had $38 million and $37 million of amounts due from unconsolidated merchant alliances included within trade accounts receivable, net in the consolidated balance sheets at September 30, 2021 and December 31, 2020, respectively. Joint Venture Transition Services Agreements Pursuant to certain transition services agreements, the Company provides, at fair value, various administration, business process outsourcing, and technical and data center related services for defined periods to certain joint ventures accounted for under the equity method. Amounts transacted through these agreements, including with InvestCloud through June 30, 2021, totaled $6 million and $16 million during the three months ended September 30, 2021 and 2020, respectively, and $32 million and $43 million during the nine months ended September 30, 2021 and 2020, respectively, and were primarily recognized as processing and services revenue in the consolidated statements of income. Share Repurchase On May 3, 2021, New Omaha Holdings L.P. (“New Omaha”), a shareholder of the Company, completed an underwritten secondary public offering of 23.0 million shares of Fiserv, Inc. common stock (the “offering”). The Company did not sell any shares in, nor did it receive any proceeds from, the offering. New Omaha received all of the net proceeds from the offering. In connection with the offering, the Company repurchased from the underwriters 5.0 million shares of its common stock that were subject to the offering, at a price equal to the price per share paid by the underwriters to New Omaha in the offering (the “share repurchase”). The share repurchase totaled $588 million and was funded with cash on hand. The repurchased shares were cancelled and no longer outstanding following the completion of the share repurchase. Prior to the offering, New Omaha owned approximately 13% of the Company’s outstanding shares of common stock, and immediately following the offering, New Omaha owned approximately 9% of such outstanding shares