Segment Information Segments - Additional Information (Detail) $ in Millions	6 Months Ended
	Jun. 30, 2025 USD ($) Integer	Dec. 31, 2024 USD ($)
Segment Reporting Information
Goodwill	$ 353.3	$ 349.1
Number of Operating Segments | Integer	3
Unum International
Segment Reporting Information
Goodwill	$ 45.6	41.4
Unum US
Segment Reporting Information
Goodwill	280.0	280.0
Colonial Life
Segment Reporting Information
Goodwill	$ 27.7	$ 27.7