v3.25.1
Assets by Segment (Detail) - USD ($)
$ in Millions
Mar. 31, 2025
Dec. 31, 2024
Segment Reporting Information    
Total Assets $ 62,459.8 $ 61,959.3
Operating Segments | Unum US    
Segment Reporting Information    
Total Assets 14,839.3 14,981.6
Operating Segments | Unum International    
Segment Reporting Information    
Total Assets 3,388.3 3,291.3
Operating Segments | Colonial Life    
Segment Reporting Information    
Total Assets 5,056.9 4,964.2
Operating Segments | Closed Block    
Segment Reporting Information    
Total Assets 33,235.6 33,376.0
Operating Segments | Corporate    
Segment Reporting Information    
Total Assets $ 5,939.7 $ 5,346.2