Condensed Consolidated Financial Statements (Policies)	3 Months Ended
Mar. 31, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Consolidation	The unaudited condensed consolidated financial statements include the accounts of ACI Worldwide, Inc. and its wholly-owned subsidiaries (collectively, the “Company”). All intercompany balances and transactions have been eliminated. The condensed consolidated financial statements as of March 31, 2021, and for the three months ended March 31, 2021 and 2020, are unaudited and reflect all adjustments of a normal recurring nature, which are, in the opinion of management, necessary for a fair presentation, in all material respects, of the financial position and operating results for the interim periods. The condensed consolidated balance sheet as of December 31, 2020, is derived from the audited financial statements. The condensed consolidated financial statements contained herein should be read in conjunction with the consolidated financial statements and notes thereto contained in the Company’s annual report on Form 10-K for the fiscal year ended December 31, 2020, filed on February 25, 2021. Results for the three months ended March 31, 2021, are not necessarily indicative of results that may be attained in the future.
Use of Estimates	The preparation of condensed consolidated financial statements in conformity with accounting principles generally accepted in the United States (“U.S. GAAP”) requires management to make judgments, estimates, and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the condensed consolidated financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates.
Settlement Assets and Liabilities	Settlement Assets and Liabilities Individuals and businesses settle their obligations to the Company’s various Biller clients using credit or debit cards or via automated clearing house (“ACH”) payments. The Company creates a receivable for the amount due from the credit or debit card processor and an offsetting payable to the client. Upon confirmation that the funds have been received, the Company settles the obligation to the client. Due to timing, in some instances, the Company may (1) receive the funds into bank accounts controlled by and in the Company’s name that are not disbursed to its clients by the end of the day, resulting in a settlement deposit on the Company’s books and (2) disburse funds to its clients in advance of receiving funds from the credit or debit card processor, resulting in a net settlement receivable position.
Off Balance Sheet Settlement Accounts	Off Balance Sheet Settlement AccountsThe Company also enters into agreements with certain Biller clients to process payment funds on their behalf. When an ACH or automated teller machine network payment transaction is processed, a transaction is initiated to withdraw funds from the designated source account and deposit them into a settlement account, which is a trust account maintained for the benefit of the Company’s clients. A simultaneous transaction is initiated to transfer funds from the settlement account to the intended destination account. These “back to back” transactions are designed to settle at the same time, usually overnight, such that the Company receives the funds from the source at the same time as it sends the funds to their destination. However, due to the transactions being with various financial institutions there may be timing differences that result in float balances. These funds are maintained in accounts for the benefit of the client, which is separate from the Company’s corporate assets. As the Company does not take ownership of the funds, these settlement accounts are not included in the Company’s balance sheet. The Company is entitled to interest earned on the fund balances. The collection of interest on these settlement accounts is considered in the Company’s determination of its fee structure for clients and represents a portion of the payment for services performed by the Company.
Fair Value	Fair ValueThe fair value of the Company’s Credit Agreement approximates the carrying value due to the floating interest rate (Level 2 of the fair value hierarchy). The Company measures the fair value of its Senior Notes based on Level 2 inputs, which include quoted market prices and interest rate spreads of similar securities.
Goodwill	Goodwill In accordance with the Accounting Standards Codification (“ASC”) 350, Intangibles – Goodwill and Other, the Company assesses goodwill for impairment annually during the fourth quarter of its fiscal year using October 1 balances or when there is evidence that events or changes in circumstances indicate that the carrying amount of the asset may not be recovered. The Company evaluates goodwill at the reporting unit level and had previously identified ACI On Demand and ACI On Premise, the operating segments at the time, as the reporting units. As of March 31, 2021, the Company's goodwill balance of $1.3 billion was allocated to these two reporting units, with $554.3 million allocated to ACI On Demand and $725.9 million allocated to ACI On Premise. Recoverability of goodwill is measured using a discounted cash flow valuation model incorporating discount rates commensurate with the risks involved. Use of a discounted cash flow model is common practice in impairment testing in the absence of available transactional market evidence to determine the fair value. The calculated fair value was substantially in excess of the current carrying value for all reporting units based upon the October 1, 2020, annual impairment test. Given the adverse economic and market conditions caused by the COVID-19 pandemic, the Company considered a variety of qualitative factors to determine if an additional quantitative impairment test was required subsequent to our annual impairment test. Based on a variety of factors, including the excess of the fair value over the carrying amount in the most recent impairment test, we determined that an additional quantitative impairment test was not required. As discussed in Note 9, Segment Information, during the first quarter of 2021, the Company made a change in organizational structure to better align with its strategic direction. This change in the Company’s operating segments will also result in a change in reporting units. The Company is currently in the process of calculating the allocation of goodwill for the new reporting units, which are expected to coincide with the new operating segments - Banks, Merchants, and Billers.
Equity Method Investment	Equity Method Investment In July 2019, the Company invested $18.3 million for a 30% non-controlling financial interest in a payment technology and services company in India. The Company accounted for this investment using the equity method in accordance with ASC 323, Investments - Equity Method and Joint Ventures. The Company records its share of earnings and losses in the investment on a one-quarter lag basis. Accordingly, the Company recorded an investment of $18.8 million and $19.3 million, which is included in other noncurrent assets in the condensed consolidated balance sheet as of March 31, 2021, and December 31, 2020, respectively.
New Accounting Standards Recently Adopted	New Accounting Standards Recently Adopted In December 2019, the Financial Accounting Standards Board ("FASB") issued Accounting Standards update ("ASU") 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes, as part of its initiative to reduce complexity in accounting standards. The amendments in this update simplify the accounting for income taxes by removing certain exceptions within ASC 740, as well as clarify and simplify other aspects of the accounting for income taxes to promote consistency among reporting entities. ASU 2019-12 was effective for annual and interim periods beginning after December 15, 2020. The adoption of ASU 2019-12 did not have a material impact on the Company's condensed consolidated financial statements.

Condensed Consolidated Financial Statements (Policies)

3 Months Ended

Mar. 31, 2021

Organization, Consolidation and Presentation of Financial Statements [Abstract]

The unaudited condensed consolidated financial statements include the accounts of ACI Worldwide, Inc. and its wholly-owned subsidiaries (collectively, the “Company”). All intercompany balances and transactions have been eliminated. The condensed consolidated financial statements as of March 31, 2021, and for the three months ended March 31, 2021 and 2020, are unaudited and reflect all adjustments of a normal recurring nature, which are, in the opinion of management, necessary for a fair presentation, in all material respects, of the financial position and operating results for the interim periods. The condensed consolidated balance sheet as of December 31, 2020, is derived from the audited financial statements.

The condensed consolidated financial statements contained herein should be read in conjunction with the consolidated financial statements and notes thereto contained in the Company’s annual report on Form 10-K for the fiscal year ended December 31, 2020, filed on February 25, 2021. Results for the three months ended March 31, 2021, are not necessarily indicative of results that may be attained in the future.

Use of Estimates

The preparation of condensed consolidated financial statements in conformity with accounting principles generally accepted in the United States (“U.S. GAAP”) requires management to make judgments, estimates, and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the condensed consolidated financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates.

Settlement Assets and Liabilities

Individuals and businesses settle their obligations to the Company’s various Biller clients using credit or debit cards or via automated clearing house (“ACH”) payments. The Company creates a receivable for the amount due from the credit or debit card processor and an offsetting payable to the client. Upon confirmation that the funds have been received, the Company settles the obligation to the client. Due to timing, in some instances, the Company may (1) receive the funds into bank accounts controlled by and in the Company’s name that are not disbursed to its clients by the end of the day, resulting in a settlement deposit on the Company’s books and (2) disburse funds to its clients in advance of receiving funds from the credit or debit card processor, resulting in a net settlement receivable position.

Off Balance Sheet Settlement Accounts

Off Balance Sheet Settlement AccountsThe Company also enters into agreements with certain Biller clients to process payment funds on their behalf. When an ACH or automated teller machine network payment transaction is processed, a transaction is initiated to withdraw funds from the designated source account and deposit them into a settlement account, which is a trust account maintained for the benefit of the Company’s clients. A simultaneous transaction is initiated to transfer funds from the settlement account to the intended destination account. These “back to back” transactions are designed to settle at the same time, usually overnight, such that the Company receives the funds from the source at the same time as it sends the funds to their destination. However, due to the transactions being with various financial institutions there may be timing differences that result in float balances. These funds are maintained in accounts for the benefit of the client, which is separate from the Company’s corporate assets. As the Company does not take ownership of the funds, these settlement accounts are not included in the Company’s balance sheet. The Company is entitled to interest earned on the fund balances. The collection of interest on these settlement accounts is considered in the Company’s determination of its fee structure for clients and represents a portion of the payment for services performed by the Company.

Fair Value

Fair ValueThe fair value of the Company’s Credit Agreement approximates the carrying value due to the floating interest rate (Level 2 of the fair value hierarchy). The Company measures the fair value of its Senior Notes based on Level 2 inputs, which include quoted market prices and interest rate spreads of similar securities.

Goodwill

In accordance with the Accounting Standards Codification (“ASC”) 350, Intangibles – Goodwill and Other, the Company assesses goodwill for impairment annually during the fourth quarter of its fiscal year using October 1 balances or when there is evidence that events or changes in circumstances indicate that the carrying amount of the asset may not be recovered. The Company evaluates goodwill at the reporting unit level and had previously identified ACI On Demand and ACI On Premise, the operating segments at the time, as the reporting units. As of March 31, 2021, the Company's goodwill balance of $1.3 billion was allocated to these two reporting units, with $554.3 million allocated to ACI On Demand and $725.9 million allocated to ACI On Premise.

Recoverability of goodwill is measured using a discounted cash flow valuation model incorporating discount rates commensurate with the risks involved. Use of a discounted cash flow model is common practice in impairment testing in the absence of available transactional market evidence to determine the fair value. The calculated fair value was substantially in excess of the current carrying value for all reporting units based upon the October 1, 2020, annual impairment test. Given the adverse economic and market conditions caused by the COVID-19 pandemic, the Company considered a variety of qualitative factors to determine if an additional quantitative impairment test was required subsequent to our annual impairment test. Based on a variety of factors, including the excess of the fair value over the carrying amount in the most recent impairment test, we determined that an additional quantitative impairment test was not required.

As discussed in Note 9, Segment Information, during the first quarter of 2021, the Company made a change in organizational structure to better align with its strategic direction. This change in the Company’s operating segments will also result in a change in reporting units. The Company is currently in the process of calculating the allocation of goodwill for the new reporting units, which are expected to coincide with the new operating segments - Banks, Merchants, and Billers.

Equity Method Investment

In July 2019, the Company invested $18.3 million for a 30% non-controlling financial interest in a payment technology and services company in India. The Company accounted for this investment using the equity method in accordance with ASC 323, Investments - Equity Method and Joint Ventures. The Company records its share of earnings and losses in the investment on a one-quarter lag basis. Accordingly, the Company recorded an investment of $18.8 million and $19.3 million, which is included in other noncurrent assets in the condensed consolidated balance sheet as of March 31, 2021, and December 31, 2020, respectively.

New Accounting Standards Recently Adopted

In December 2019, the Financial Accounting Standards Board ("FASB") issued Accounting Standards update ("ASU") 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes, as part of its initiative to reduce complexity in accounting standards. The amendments in this update simplify the accounting for income taxes by removing certain exceptions within ASC 740, as well as clarify and simplify other aspects of the accounting for income taxes to promote consistency among reporting entities. ASU 2019-12 was effective for annual and interim periods beginning after December 15, 2020. The adoption of ASU 2019-12 did not have a material impact on the Company's condensed consolidated financial statements.