v3.21.2

Financial Instruments - Warrants - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions |  | 3 Months Ended | 9 Months Ended
--- | --- | --- | ---
May 26, 2020 | Sep. 30, 2021 | Sep. 30, 2021
Class Of Warrant Or Right [Line Items] |  |  |
Warrants outstanding |  | 59,633,274 | 59,633,274
Warrants expiration date |  | Jul. 02, 2026 | Jul. 02, 2026
Warrants expiration term |  | 5 years | 5 years
Fair value of warrants |  | $ 182 | $ 182
Loss (gain) from change in fair value of warrant liabilities |  | $ 55 |
Redemption of Warrants When the Price per Share of Class A Common Stock Equals or Exceeds $18.00 |  |  |
Class Of Warrant Or Right [Line Items] |  |  |
Redemption price per warrant (in dollars per share) |  |  | $ 0.01
Stock price trigger for redemption of warrants (in dollars per share) |  |  | 18.00
Redemption of Warrants When Price per Share of Class A Common Stock Greater than 10.00 but Less than 18.00 |  |  |
Class Of Warrant Or Right [Line Items] |  |  |
Redemption price per warrant (in dollars per share) |  |  | 0.10
Redemption of Warrants When Price per Share of Class A Common Stock Greater than 10.00 but Less than 18.00 | Minimum |  |  |
Class Of Warrant Or Right [Line Items] |  |  |
Stock price trigger for redemption of warrants (in dollars per share) |  |  | 10.00
Redemption of Warrants When Price per Share of Class A Common Stock Greater than 10.00 but Less than 18.00 | Maximum |  |  |
Class Of Warrant Or Right [Line Items] |  |  |
Stock price trigger for redemption of warrants (in dollars per share) |  |  | $ 18.00
Private Placement Warrants |  |  |
Class Of Warrant Or Right [Line Items] |  |  |
Number of shares issuable per warrant |  | 1 | 1
Private Placement Warrants | Class A Common Stock |  |  |
Class Of Warrant Or Right [Line Items] |  |  |
Share price per share |  | $ 11.50 | $ 11.50
FTAC | Private Placement Warrants |  |  |
Class Of Warrant Or Right [Line Items] |  |  |
Number of warrants issued | 15,133,333 |  |
FTAC | Public Warrants |  |  |
Class Of Warrant Or Right [Line Items] |  |  |
Number of warrants issued | 34,499,941 |  |
FTAC | Forward Purchase Warrants |  |  |
Class Of Warrant Or Right [Line Items] |  |  |
Number of warrants to be purchased | 10,000,000 |  |

X
- Definition Price of the entity's common stock which would be required to be attained to trigger the redemption of warrants. + References No definition available. + Details
Name: | alit_ClassOfWarrantOrRightRedemptionOfWarrantsOrRightsStockPriceTrigger
Namespace Prefix: | alit_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | duration

X
- Definition Redemption price per share or per unit of warrants or rights outstanding. + References No definition available. + Details
Name: | alit_ClassOfWarrantOrRightRedemptionPriceOfWarrantsOrRights
Namespace Prefix: | alit_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the number of warrants issued. + References No definition available. + Details
Name: | alit_NumberOfWarrantsIssued
Namespace Prefix: | alit_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration

X
- Definition This represents warrants to be purchased pursuant to agreements. + References No definition available. + Details
Name: | alit_WarrantsToBePurchasedPursuantToAgreements
Namespace Prefix: | alit_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | instant

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_ClassOfWarrantOrRightLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Number of securities into which each warrant or right may be converted. For example, but not limited to, each warrant may be converted into two shares. + References No definition available. + Details
Name: | us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByEachWarrantOrRight
Namespace Prefix: | us-gaap_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | instant

X
- Definition Number of warrants or rights outstanding. + References No definition available. + Details
Name: | us-gaap_ClassOfWarrantOrRightOutstanding
Namespace Prefix: | us-gaap_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | instant

X
- Definition Amount of expense (income) related to adjustment to fair value of warrant liability. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3602-108585 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 480 -SubTopic 10 -Section 25 -Paragraph 13 -URI http://asc.fasb.org/extlink&oid=109262497&loc=d3e20148-110875 + Details
Name: | us-gaap_FairValueAdjustmentOfWarrants
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Price of a single share of a number of saleable stocks of a company. + References No definition available. + Details
Name: | us-gaap_SharePrice
Namespace Prefix: | us-gaap_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | instant

X
- Definition The fair value of shares that would be issued, determined under the conditions specified in the contract if the settlement were to occur at the reporting date. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 480 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=109262807&loc=d3e22047-110879 + Details
Name: | us-gaap_SharesSubjectToMandatoryRedemptionSettlementTermsFairValueOfShares
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Expiration date of outstanding warrant and right embodying unconditional obligation requiring redemption by transferring asset at specified or determinable date or upon event certain to occur, in CCYY-MM-DD format. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (bbb)(2) -URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258 + Details
Name: | us-gaap_WarrantsAndRightsOutstandingMaturityDate
Namespace Prefix: | us-gaap_
Data Type: | xbrli:dateItemType
Balance Type: | na
Period Type: | instant

X
- Definition Period between issuance and expiration of outstanding warrant and right embodying unconditional obligation requiring redemption by transferring asset at specified or determinable date or upon event certain to occur, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (bbb)(2) -URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258 + Details
Name: | us-gaap_WarrantsAndRightsOutstandingTerm
Namespace Prefix: | us-gaap_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | instant

X
- Details
Name: | srt_StatementScenarioAxis=alit_RedemptionOfWarrantsWhenPricePerShareOfClassCommonStockEqualsOrExceeds1800Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_StatementScenarioAxis=alit_RedemptionOfWarrantsWhenPricePerShareOfClassCommonStockGreaterThan1000ButLessThan1800Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_RangeAxis=srt_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_RangeAxis=srt_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ClassOfWarrantOrRightAxis=alit_PrivatePlacementWarrantsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementClassOfStockAxis=us-gaap_CommonClassAMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | dei_LegalEntityAxis=alit_FtacMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ClassOfWarrantOrRightAxis=alit_PublicWarrantsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ClassOfWarrantOrRightAxis=alit_ForwardPurchaseWarrantsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |