v3.21.2

Segment Reporting - Additional Information (Details) - Customer | 9 Months Ended
--- | ---
Sep. 30, 2021 | Sep. 30, 2020
Segment Reporting [Abstract] |  |
Number of single client comprising more than 10% of revenues | 0 | 0

X
- Definition Number of single client comprising more than ten percent of revenues. + References No definition available. + Details
Name: | alit_NumberOfSingleClientComprisingMoreThanTenPercentOfRevenues
Namespace Prefix: | alit_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- References No definition available. + Details
Name: | us-gaap_SegmentReportingAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration