Fair Value Measurement - Reconciliation of TRA Liability and Seller Earnout Liability (Details) $ in Millions	6 Months Ended
Dec. 31, 2021 USD ($)
Tax Receivable Agreement Liability
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Beginning Balance	$ 618
Gain from change in fair value of TRA	(37)
Ending Balance	581
Seller Earnouts Liability
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Beginning Balance	109
Loss from change in fair value of Seller Earnouts	26
Ending Balance	$ 135

Fair value measurement with unobservable inputs reconciliation recurring basis liability gain from change in fair value of TRA.

No definition available.

+ Details

Name:	alit_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainFromChangeInFairValueOfTRA
Namespace Prefix:	alit_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Fair value, measurement with unobservable inputs reconciliation, recurring basis liability loss from change in fair value of seller earnouts.

+ References

No definition available.

+ Details

Name:	alit_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityLossFromChangeInFairValueOfSellerEarnouts
Namespace Prefix:	alit_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- 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_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Fair value of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=123874694&loc=d3e19207-110258

+ Details

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_FairValueByLiabilityClassAxis=alit_TaxReceivableAgreementLiabilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByLiabilityClassAxis=alit_SellerEarnoutsLiabilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: