Segment Information Segments - Additional Information (Detail) $ in Millions	3 Months Ended
	Mar. 31, 2026 USD ($) Integer	Dec. 31, 2025 USD ($)
Segment Reporting
Goodwill	$ 353.0	$ 353.9
Number of Operating Segments | Integer	3
Unum US
Segment Reporting
Goodwill	$ 281.2	281.2
Colonial Life
Segment Reporting
Goodwill	27.7	27.7
Unum International
Segment Reporting
Goodwill	$ 44.1	$ 45.0