Assets by Segment (Detail) - USD ($) $ in Millions	Jun. 30, 2022	Dec. 31, 2021
Segment Reporting Information
Total Assets	$ 63,121.1	$ 70,115.6
Operating Segments | Unum US
Segment Reporting Information
Total Assets	16,743.8	18,696.3
Operating Segments | Unum International
Segment Reporting Information
Total Assets	3,386.8	4,086.5
Operating Segments | Colonial Life
Segment Reporting Information
Total Assets	4,594.7	4,895.9
Operating Segments | Closed Block
Segment Reporting Information
Total Assets	34,439.3	38,287.9
Operating Segments | Corporate
Segment Reporting Information
Total Assets	$ 3,956.5	$ 4,149.0