Financial Instruments	3 Months Ended
Financial Instruments	Mar. 31, 2025
Financial Instruments [Abstract]
Financial Instruments	14. Financial Instruments Seller Earnouts Upon completion of the Business Combination, the equity owners of Alight Holdings received an earnout in the form of non-voting shares of Class B-1 and Class B-2 Common Stock, which automatically convert into Class A Common Stock if, at any time during the seven years following the Closing Date, certain criteria are achieved. See Note 9 “Stockholders’ Equity” for additional information regarding the Seller Earnouts. The portion of the Seller Earnouts related to employee compensation was accounted for as share-based compensation. As all employee compensation associated with the Seller Earnouts was ultimately vested on July 2, 2024, no portion of the Seller Earnout as of March 31, 2025 was accounted for as share-based compensation. See Note 10 “Share-Based Compensation” for additional information. As of March 31, 2025, all of the remaining Seller Earnouts were accounted for as a contingent consideration liability at fair value within Financial instruments on the Condensed Consolidated Balance Sheets because the Seller Earnouts do not meet the criteria for classification within equity. This liability is subject to remeasurement at each balance sheet date. At March 31, 2025 and December 31, 2024, the Seller Earnouts had a fair value of $29 million and $51 million, respectively. For the three months ended March 31, 2025 and 2024, the fair value remeasurement of the Seller Earnouts resulted in a gain of $22 million and loss of $19 million, respectively. Gains or losses related to the remeasurement of Seller Earnouts are recorded in (Gain) Loss from change in fair value of financial instruments within the accompanying Condensed Consolidated Statements of Comprehensive Income (Loss). The fair value of the Class B-1 and B-2 Seller Earnouts, and, prior to the Class Z vesting on July 2, 2024, the Class Z-B-1 and Z-B-2 contingent consideration instruments, is determined using Monte Carlo simulation and Option Pricing Methods (Level 3 inputs, see Note 16 "Fair Value Measurement"). Significant unobservable inputs are used in the assessment of fair value, including the following assumptions: volatility of 39.00%, risk-free interest rate of 3.90%, expected holding period of 3.26 years, dividend participation, and probability assessments based on the likelihood of reaching the performance targets defined in the Business Combination. A decrease in the risk-free interest rate or expected volatility would result in a decrease in the fair value measurement of the Seller Earnouts and vice versa. As discussed in Note 9 “Stockholders’ Equity”, in connection with the ultimate forfeiture of the shares of unvested Class A, unvested Class B-1, and unvested Class B-2 common stock issued to participating management holders on July 2, 2024, all Class Z instruments were ultimately settled resulting in the re-allocation of the forfeited compensatory Class A, Class B-1 and Class B-2 instruments. The Class Z instruments are also accounted for as a contingent consideration liability at fair value within Financial instruments on the Condensed Consolidated Balance Sheets because these instruments do not meet the criteria for classification within equity. The fair value of the Class Z-A contingent consideration was determined using the ending share price as of the last day of each quarter until settlement on July 2, 2024, resulting in the issuance of 1.5 million shares of Class A common stock and units at the $7.09 stock price on that date. At March 31, 2025 and December 31, 2024, the Class Z-A contingent consideration was no longer outstanding. For the three months ended March 31, 2025 and 2024, the Company recorded no loss and a loss of $2 million, respectively, in (Gain) Loss from change in fair value of financial instruments in the Condensed Consolidated Statements of Comprehensive Income (Loss) as a result of the forfeiture of unvested management equity that was ultimately re-allocated to the holders of Class Z instruments on July 2, 2024. See Note 9 “Stockholders’ Equity” for additional information regarding these instruments. Additional Seller Note As disclosed above in Note 1 “Basis of Presentation and Nature of Business”, on July 12, 2024, the Company closed on the Divestiture. As part of the sale, the Company received a note with an aggregate principal amount of up to $150 million (the “Additional Seller Note”) with an initial fair value of $43 million as of July 12, 2024 to be issued by the Note Issuer. See Note 4 “Discontinued Operations” for additional information. The Additional Seller Note is considered a level 3 recurring fair value measurement. At March 31, 2025 and December 31, 2024, the Additional Seller Note had a fair value of $36 million and $50 million, respectively. For the three months ended March 31, 2025, the Company recorded a loss of $14 million from the fair value remeasurement of the Additional Seller Note. For the three months ended March 31, 2024, no gains or losses were recorded as the closing date of the Transaction was July 12, 2024. Gains or losses related to the recurring fair value remeasurement of the Additional Seller Note are recorded in (Gain) Loss from change in fair value of financial instruments within the accompanying Condensed Consolidated Statements of Comprehensive Income (Loss). The fair value of the Additional Seller Note is determined using a variation of the income approach (Level 3 inputs, see Note 16 "Fair Value Measurement"). Significant unobservable inputs are used in the assessment of fair value, including the following assumptions: expected Adjusted EBITDA, expected maturity of 5.28 years for the Additional Seller Note, the Divested Business's estimated cost of debt, and based on the likelihood of reaching the performance targets defined in the Purchase Agreement.