Costs Related to Organizational Design Update (Details) $ in Millions	3 Months Ended
Sep. 30, 2020 USD ($)
Organizational Design Updates [Abstract]
Costs Related to Organizational Design Update	$ 23.3

Amount charged during the period for costs incurred related to organizational design update

No definition available.

Name:	unm_CostsRelatedToOrganizationalDesignUpdate
Namespace Prefix:	unm_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration