Related Party Transactions	12 Months Ended
Related Party Transactions	Dec. 31, 2020
Related Party Transactions [Abstract]
Related Party Transactions	Related Party Transactions Merchant Alliances A significant portion of the Company’s business is conducted through merchant alliances between the Company and financial institutions (see Note 9). 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 Company’s consolidated revenues include processing fees, administrative service fees, and other fees charged to alliances accounted for under the equity method. Such fees totaled $183 million and $76 million for the years ended December 31, 2020 and 2019, 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 bank 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 bank 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. At December 31, 2020 and 2019, the Company had approximately $37 million and $35 million, respectively, of amounts due from unconsolidated merchant alliances included within trade accounts receivable, net in the Company’s consolidated balance sheets. Effective July 1, 2020, the Company and Bank of America dissolved their BAMS joint venture, of which the Company maintained a 51% controlling ownership interest. Upon dissolution of the joint venture’s operations, the joint venture transferred a proportionate share of value, primarily the client contracts, to each party via an agreed upon contractual separation. The revenues and expenses of the BAMS joint venture were consolidated into the Company’s financial results through the date of dissolution. See Note 4 for additional information. 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 the Lending Joint Ventures and Tegra 118 (see Note 4). Amounts transacted through these agreements totaled $58 million, $36 million and $30 million during the years ended December 31, 2020, 2019 and 2018, respectively, and were primarily recognized as processing and services revenue in the Company’s consolidated statements of income. Share Repurchase On December 14, 2020, New Omaha Holdings L.P. (“New Omaha”), a shareholder of the Company, completed an underwritten secondary public offering of 20.1 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 1.8 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 $200 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 16% of the Company’s outstanding shares of common stock, and following the offering, New Omaha owned approximately 13% as of December 31, 2020.