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

Number of single client comprising more than ten percent of revenues.

No definition available.

Name:	alit_NumberOfSingleClientComprisingMoreThanTenPercentOfRevenues
Namespace Prefix:	alit_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration