Basis of Presentation (Policies)	9 Months Ended
Basis of Presentation (Policies)	Sep. 30, 2018
Accounting Policies [Abstract]
Principles of Consolidation, Policy	Principles of Consolidation The consolidated financial statements include the accounts of Fiserv, Inc. and all 100% owned subsidiaries. Investments in less than 50% owned affiliates in which the Company has significant influence but not control are accounted for using the equity method of accounting. All intercompany transactions and balances have been eliminated in consolidation.
Recently Adopted And Issued Accounting Pronouncements, Policy	Recent Accounting Pronouncements Recently Adopted Accounting Pronouncements In February 2018, the Financial Accounting Standards Board (“FASB”) issued ASU No. 2018-02, Income Statement - Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income (“ASU 2018-02”), which allows a reclassification from accumulated other comprehensive income to retained earnings for stranded tax effects of the change in the U.S. federal corporate tax rate resulting from The Tax Cuts and Jobs Act (the “Tax Act”) enacted in December 2017. ASU 2018-02 is effective for fiscal years, including interim periods within those fiscal years, beginning after December 15, 2018, with early adoption permitted. The Company early adopted ASU 2018-02 in the first quarter of 2018, and elected to reclassify the Tax Act income tax benefits of $3 million from accumulated other comprehensive loss to retained earnings. In August 2017, the FASB issued ASU No. 2017-12, Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities (“ASU 2017-12”), which provides guidance designed to improve the financial reporting of hedging relationships to better portray the economic results of an entity’s risk management activities in its financial statements as well as to simplify the application of the hedge accounting guidance in current U.S. generally accepted accounting principles. For public entities, ASU 2017-12 is effective for fiscal years, including interim periods within those fiscal years, beginning after December 15, 2018, with early adoption permitted in any interim period or fiscal year. For cash flow and net investment hedges existing at the date of adoption, the standard requires a cumulative-effect adjustment to eliminate the separate measurement of ineffectiveness to accumulated other comprehensive income with a corresponding adjustment to the opening balance of retained earnings as of the beginning of the fiscal year of adoption. The amended presentation and disclosure guidance is required only prospectively. The Company early adopted ASU 2017-12 in the first quarter of 2018, and recorded a cumulative-effect adjustment to accumulated other comprehensive loss of $3 million with a corresponding decrease in the opening balance of retained earnings. In October 2016, the FASB issued ASU No. 2016-16, Income Taxes (Topic 740): Intra-Entity Transfers of Assets Other Than Inventory (“ASU 2016-16”), which eliminates the current prohibition on immediate recognition of the current and deferred income tax effects of intra-entity transfers of assets other than inventory, with the intent of reducing complexity and diversity in practice. Under ASU 2016-16, entities must recognize the income tax consequences when the transfer occurs rather than deferring recognition. For public entities, ASU 2016-16 is effective for fiscal years, including interim periods within those fiscal years, beginning after December 15, 2017. Entities must apply the guidance on a modified retrospective basis through a cumulative-effect adjustment to retained earnings as of the beginning of the period of adoption. The Company adopted ASU 2016-16 in the first quarter of 2018, and the adoption did not have a material impact on its consolidated financial statements. In January 2016, the FASB issued ASU No. 2016-01, Recognition and Measurement of Financial Assets and Financial Liabilities (“ASU 2016-01”), which primarily affects the accounting for equity investments, financial liabilities under the fair value option, and the presentation and disclosure requirements of financial instruments. For public entities, ASU 2016-01 is effective for fiscal years, and interim periods within those years, beginning after December 15, 2017. Entities must apply the standard, with certain exceptions, using a cumulative-effect adjustment to beginning retained earnings as of the beginning of the fiscal year of adoption. The Company adopted ASU 2016-01 in the first quarter of 2018, and the adoption did not have any impact on its consolidated financial statements. In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers (“ASU 2014-09”), to clarify the principles of recognizing revenue and to create common revenue recognition guidance between U.S. generally accepted accounting principles and International Financial Reporting Standards. ASU 2014-09 outlines a single comprehensive model for entities to use in accounting for revenue arising from contracts with customers and supersedes most current revenue recognition guidance, including industry-specific requirements. It also includes guidance on accounting for the incremental costs of obtaining and costs incurred to fulfill a contract with a customer. The core principle of the revenue model is that an entity recognizes revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. This model involves a five-step process for achieving that core principle, along with comprehensive disclosures about the nature, amount, timing and uncertainty of revenue and cash flows arising from contracts with customers. For public entities, the new revenue standard is effective for annual and interim periods beginning after December 15, 2017. Entities have the option of adopting this new guidance using either a full retrospective or a modified approach with the cumulative effect of applying the guidance recognized at the date of initial application. The Company adopted the new standard effective January 1, 2018 using the modified retrospective transition approach applied to all contracts, which resulted in a cumulative-effect increase in the opening balance of retained earnings of $208 million, primarily related to the deferral of incremental sales commissions incurred in obtaining contracts in prior periods. Under this transition approach, the Company has not restated the prior period consolidated financial statements presented; however, it has provided additional disclosures related to the amount by which each relevant 2018 financial statement line item was affected by adoption of the new standard and explanations for significant changes (see Note 3). Recently Issued Accounting Pronouncements In August 2018, the FASB issued ASU No. 2018-15, Intangibles - Goodwill and Other - Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract (“ASU 2018-15”), which aligns the requirements for capitalizing implementation costs incurred in a cloud computing hosting arrangement that is a service contract with the requirements under Accounting Standards Codification (“ASC”) 350 for capitalizing implementation costs incurred to develop or obtain internal-use software. For public entities, ASU 2018-15 is effective for fiscal years, and interim periods within those years, beginning after December 15, 2019, with early adoption permitted. Entities are permitted to apply either a retrospective or prospective transition approach to adopt the guidance. The Company is currently assessing the impact that the adoption of ASU 2018-15 will have on its consolidated financial statements. In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement (“ASU 2018-13”), which removes, modifies, and adds certain disclosure requirements of ASC Topic 820, Fair Value Measurement. ASU 2018-13 is effective for fiscal years, including interim periods within those fiscal years, beginning after December 15, 2019, with the additional disclosures required to be applied prospectively and the modified and removed disclosures required to be applied retrospectively to all periods presented. Entities are permitted to early adopt the removed or modified disclosures and delay the adoption of the additional disclosures until the effective date. The Company is currently assessing the impact that the adoption of ASU 2018-13 will have on its consolidated financial statements. In June 2018, the FASB issued ASU No. 2018-07, Compensation - Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting (“ASU 2018-07”), which simplifies the accounting for share-based payments granted to nonemployees by largely aligning it with the accounting for share-based payments to employees. For public entities, ASU 2018-07 is effective for fiscal years, and interim periods within those years, beginning after December 15, 2018, with early adoption permitted. Entities must apply the standard, using a modified retrospective transition approach, with a cumulative-effect adjustment to retained earnings as of the beginning of the fiscal year of adoption for all liability-classified nonemployee awards that have not been settled as of the adoption date and equity-classified nonemployee awards for which a measurement date has not been established. The Company plans to adopt ASU 2018-07 on January 1, 2019 and does not expect the adoption to have a material impact on its consolidated financial statements. In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments - Credit Losses (Topic 326) (“ASU 2016-13”), which prescribes an impairment model for most financial assets based on expected losses rather than incurred losses. Under this model, an estimate of expected credit losses over the contractual life of the instrument is to be recorded as of the end of a reporting period as an allowance to offset the amortized cost basis, resulting in a net presentation of the amount expected to be collected on the financial asset. For public entities, ASU 2016-13 is effective for fiscal years, including interim periods within those fiscal years, beginning after December 15, 2019. Early adoption is permitted for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. For most instruments, entities must apply the standard using a cumulative-effect adjustment to beginning retained earnings as of the beginning of the fiscal year of adoption. The Company is currently assessing the impact that the adoption of ASU 2016-13 will have on its consolidated financial statements. In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) (“ASU 2016-02”), which requires lessees to recognize a lease liability and a right-of-use asset for each lease with a term longer than twelve months. The recognized liability is measured at the present value of lease payments not yet paid, and the corresponding asset represents the lessee’s right to use the underlying asset over the lease term and is based on the liability, subject to certain adjustments. For income statement purposes, the standard retains the dual model with leases classified as either operating or finance. Operating leases will result in straight-line expense while finance leases will result in a front-loaded expense pattern. The standard prescribes a modified retrospective transition approach for leases existing at, or entered into after, the beginning of the earliest comparative period presented in the financial statements. In July 2018, the FASB issued ASU No. 2018-11, Leases (Topic 842) - Targeted Improvements (“ASU 2018-11”), which provides an additional transition method allowing entities to initially apply the new lease standard at the adoption date and recognize a cumulative-effect adjustment to the opening balance of retained earnings in the period of adoption. For public entities, ASU 2016-02 is effective for annual and interim periods beginning after December 15, 2018, with early adoption permitted. The Company continues to review the requirements of the new lease standard, including the activity of the FASB as it relates to interpretive guidance and additional practical expedients. The Company has formed a cross-functional project team which is currently in the process of evaluating its existing lease arrangements and assessing potential impacts of adopting the new lease standard on its consolidated financial statements, related disclosures, accounting policies, process and system changes, and controls. The Company has completed the planning and design phases of the project, including the selection of a lease accounting software solution to comply with the new standard, and has engaged an implementation partner to assist with the adoption. While the Company continues to evaluate other practical expedients available under the guidance, it expects to elect the package of practical expedients permitted under the transition guidance within ASU 2016-02 to not reassess prior conclusions related to contracts containing leases, lease classification and initial direct costs and, therefore, does not anticipate a material impact on its consolidated statements of income. While the Company is continuing to assess the effects of adoption, it currently believes the most significant changes relate to the recognition of right-of-use assets and lease liabilities on its consolidated balance sheets for real and personal property operating leases, as well as the impact of new disclosure requirements. The Company plans to adopt ASU 2016-02 on January 1, 2019 and anticipates using the optional transition method in ASU 2018-11. Under this method, the Company would not adjust its comparative period financial statements for the effects of the new standard or make the new required lease disclosures for periods prior to the effective date.
Revenue from Contract with Customer, Policy	Contract assets, reported within other long-term assets in the consolidated balance sheet, primarily result from revenue being recognized where payment is contingent upon the transfer of services to a customer over the contractual period. Contract liabilities primarily relate to advance consideration received from customers (deferred revenue) for which transfer of control occurs, and therefore revenue is recognized, as services are provided. Contract balances are reported in a net contract asset or liability position on a contract-by-contract basis at the end of each reporting period. The Company generates revenue from the delivery of processing, service and product solutions. Revenue is measured based on consideration specified in a contract with a customer, and excludes any amounts collected on behalf of third parties. The Company recognizes revenue when it satisfies a performance obligation by transferring control over a product or service to a customer which may be at a point in time or over time. Taxes assessed by a governmental authority that are both imposed on and concurrent with a specific revenue-producing transaction, that are collected by the Company from a customer, are excluded from revenue. Shipping and handling activities associated with outbound freight after control over a product has transferred to a customer are accounted for as a fulfillment activity and recognized as revenue at the point in time at which control of the goods transfers to the customer. As a practical expedient, the Company does not adjust the transaction price for the effects of a significant financing component if, at contract inception, the period between customer payment and the transfer of goods or services is expected to be one year or less. Nature of Goods and Services The Company’s operations are comprised of the Payments and Industry Products (“Payments”) segment and the Financial Institution Services (“Financial”) segment. Additional information regarding the Company’s business segments is included in Note 16. The following is a description of principal activities from which the Company generates its revenue. Contracts with customers are evaluated on a contract-by-contract basis as contracts may include multiple types of goods and services as described below. Processing and Services Processing and services revenue is generated from account- and transaction-based fees for data processing, transaction processing, electronic billing and payment services, electronic funds transfer and debit processing services; consulting and professional services; and software maintenance for ongoing client support. The Company recognizes processing and services revenues in the period in which the specific service is performed unless they are not deemed distinct from other goods or services in which revenue would then be recognized as control is transferred of the combined goods and services. The Company’s arrangements for processing and services typically consist of an obligation to provide specific services to its customers on a when and if needed basis (a stand-ready obligation) and revenue is recognized from the satisfaction of the performance obligations in the amount billable to the customer. These services are typically provided under a fixed or declining (tier-based) price per unit based on volume of service, however, may also be based on minimum monthly usage fees. Fees for the Company’s processing and services arrangements are typically billed and paid on a monthly basis. Product Product revenue is generated from integrated print and card production sales, as well as software license sales. For software license agreements that are distinct, the Company recognizes software license revenue upon delivery, assuming a contract is deemed to exist. Revenue for arrangements with customers that include significant customization, modification or production of software such that the software is not distinct is typically recognized over time based upon efforts expended, such as labor hours, to measure progress towards completion. For arrangements involving hosted licensed software for the customer, a software element is considered present to the extent the customer has the contractual right to take possession of the software at any time during the hosting period without significant penalty and it is feasible for the customer to either operate the software on their own hardware or contract with another vendor to host the software. Significant Judgments in Application of the Guidance The Company uses the following methods, inputs, and assumptions in determining amounts of revenue to recognize: Identification of Performance Obligations For multi-element arrangements, the Company accounts for individual goods or services as a separate performance obligation if they are distinct, the good or service is separately identifiable from other items in the arrangement, and if a customer can benefit from it on its own or with other resources that are readily available to the customer. If these criteria are not met, the promised goods or services are accounted for as a combined performance obligation. Technology or service components from third parties are frequently embedded in or combined with the Company’s applications or service offerings. Whether the Company recognizes revenue based on the gross amount billed to a customer or the net amount retained involves judgment that depends on the relevant facts and circumstances including the level of contractual responsibilities and obligations for delivering solutions to end customers. Determination of Transaction Price The transaction price is determined based on the consideration to which the Company will be entitled in exchange for transferring products or services to the customer. The Company includes any fixed charges within its contracts as part of the total transaction price. To the extent that variable consideration is not constrained, the Company includes an estimate of the variable amount, as appropriate, within the total transaction price and updates its assumptions over the duration of the contract. Assessment of Estimates of Variable Consideration Many of the Company’s contracts with customers contain some component of variable consideration; however, the constraint will generally not result in a reduction in the estimated transaction price for most forms of variable consideration. The Company may constrain the estimated transaction price in the event of a high degree of uncertainty as to the final consideration amount owed because of an extended length of time over which the fees may be adjusted. Allocation of Transaction Price The transaction price (including any discounts) is allocated between separate goods and services in a multi-element arrangement based on their relative standalone selling prices. The standalone selling prices are determined based on the prices at which the Company separately sells each good or service. For items that are not sold separately, the Company estimates the standalone selling prices using available information such as market conditions and internally approved pricing guidelines. In instances where there are observable selling prices for professional services and support and maintenance, the Company may apply the residual approach to estimate the standalone selling price of software licenses. In certain situations, primarily processing and services revenue described above, the Company allocates variable consideration to a distinct good(s) or service(s) within a contract. The Company allocates variable payments to one or more, but not all, of the distinct goods or services in a contract when (i) the variable payment relates specifically to the Company’s efforts to transfer the distinct good or service and (ii) the variable payment is for an amount that depicts the amount of consideration to which the Company expects to be entitled in exchange for transferring the promised goods or services to its customer. Revenue Recognition During the Three and Nine Months Ended September 30, 2017 The Company generates revenue from the delivery of processing, service and product solutions. Revenue is recognized when written contracts are signed, delivery has occurred, the fees are fixed or determinable, and collectability is reasonably assured. Processing and services revenue is recognized as services are provided and is primarily derived from contracts that generate account- and transaction-based fees for data processing, transaction processing, electronic billing and payment services, electronic funds transfer and debit processing services. In addition, processing and services revenue is derived from the fulfillment of professional services, including consulting activities. Certain of the Company’s revenue is generated from multiple element arrangements involving various combinations of product and service deliverables. The deliverables within these arrangements are evaluated at contract inception to determine whether they represent separate units of accounting, and if so, contract consideration is allocated to each deliverable based on relative selling price. The relative selling price is determined using vendor specific objective evidence of fair value, third-party evidence or best estimate of selling price. Revenue is then recognized in accordance with the appropriate revenue recognition guidance applicable to the respective elements. Also included in processing and services revenue is software maintenance fee revenue for ongoing client support, which is recognized ratably over the term of the applicable support period, generally 12 months. Contract liabilities consist primarily of advance cash receipts for services (deferred revenue) and are recognized as revenue when the services are provided. Product revenue is primarily derived from integrated print and card production sales, as well as software license sales which represented less than 4% of consolidated revenue. For software license agreements that do not require significant customization or modification, the Company recognizes software license revenue upon delivery, assuming persuasive evidence of an arrangement exists, the license fee is fixed or determinable, and collection is reasonably assured. Arrangements with customers that include significant customization, modification or production of software are accounted for under contract accounting, with revenue recognized using the percentage-of-completion method based upon efforts expended, such as labor hours, to measure progress towards completion. Changes in estimates for revenues, costs and profits are recognized in the period in which they are determinable and were not material for any period presented. The Company includes reimbursements from clients, such as postage and telecommunication costs, in processing and services revenue and product revenue, while the related costs are included in cost of processing and services and cost of product. Capitalized contract costs are amortized based on the transfer of goods or services to which the asset relates. The amortization period also considers expected customer lives and whether the asset relates to goods or services transferred under a specific anticipated contract. The Company applies the optional exemption in paragraph 606-10-50-14(b) and does not disclose information about remaining performance obligations for account- and transaction-based processing fees that qualify for recognition in accordance with paragraph 606-10-55-18. These contracts generally have terms of three to five years, and contain variable consideration for stand-ready performance obligations for which the exact quantity and mix of transactions to be processed are contingent upon the customer’s request. The Company also applies the optional exemptions in paragraph 606-10-50-14A and does not disclose information for variable consideration, including additional seat licenses, that is a sales-based or usage-based royalty promised in exchange for a license of intellectual property or that is allocated entirely to a wholly unsatisfied performance obligation or to a wholly unsatisfied promise to transfer a distinct good or service in a series. The amounts disclosed above as remaining performance obligations consist primarily of fixed or monthly minimum processing fees and maintenance fees under contracts with an original expected duration of greater than one year. Contract Costs The Company incurs incremental costs to obtain a contract as well as costs to fulfill contracts with customers that are expected to be recovered. These costs consist primarily of sales commissions incurred only if a contract is obtained, and customer conversion or implementation related costs.