Deferred Policy Acquisition Costs (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Movement Analysis of Deferred Policy Acquisition Costs
Deferred Acquisition Costs at Beginning of Year		$ 2,842.8
Amortization expense		(527.1)	$ (521.0)	$ (481.4)
Deferred Acquisition Costs at End of Year		2,920.3	2,842.8
Operating Segments
Movement Analysis of Deferred Policy Acquisition Costs
Deferred Acquisition Costs at Beginning of Year		2,842.8	2,714.5	2,560.0
Capitalization		697.1	651.5	632.2
Amortization expense		(527.1)	(521.0)	(481.4)
Foreign currency		7.8	(2.2)	3.7
Deferred Acquisition Costs at End of Year		2,920.3	2,842.8	2,714.5
Operating Segments | Long-term Care and Individual Disability Reinsurance Transaction
Movement Analysis of Deferred Policy Acquisition Costs
Change in Deferred Acquisition Costs	[1]	(100.3)
Unum US
Movement Analysis of Deferred Policy Acquisition Costs
Deferred Acquisition Costs at Beginning of Year		1,260.6	1,232.2	1,185.1
Capitalization		331.7	320.9	314.7
Amortization expense		(283.3)	(292.5)	(267.6)
Foreign currency		0.0	0.0	0.0
Deferred Acquisition Costs at End of Year		1,208.7	1,260.6	1,232.2
Unum US | Long-term Care and Individual Disability Reinsurance Transaction
Movement Analysis of Deferred Policy Acquisition Costs
Change in Deferred Acquisition Costs	[1]	(100.3)
Unum US | Operating Segments
Movement Analysis of Deferred Policy Acquisition Costs
Amortization expense		(283.3)	(292.5)	(267.6)
Unum International
Movement Analysis of Deferred Policy Acquisition Costs
Deferred Acquisition Costs at Beginning of Year		53.0	46.9	37.0
Capitalization		22.0	17.8	14.6
Amortization expense		(10.7)	(9.5)	(8.4)
Foreign currency		7.8	(2.2)	3.7
Deferred Acquisition Costs at End of Year		72.1	53.0	46.9
Unum International | Operating Segments
Movement Analysis of Deferred Policy Acquisition Costs
Amortization expense		(10.7)	(9.5)	(8.4)
Colonial Life
Movement Analysis of Deferred Policy Acquisition Costs
Deferred Acquisition Costs at Beginning of Year		1,529.2	1,435.4	1,337.9
Capitalization		343.4	312.8	302.9
Amortization expense		(233.1)	(219.0)	(205.4)
Foreign currency		0.0	0.0	0.0
Deferred Acquisition Costs at End of Year		1,639.5	1,529.2	1,435.4
Colonial Life | Operating Segments
Movement Analysis of Deferred Policy Acquisition Costs
Amortization expense		(233.1)	(219.0)	(205.4)
Group Disability | Unum US
Movement Analysis of Deferred Policy Acquisition Costs
Deferred Acquisition Costs at Beginning of Year		61.1	63.6	61.0
Capitalization		60.7	62.2	60.2
Amortization expense		(58.2)	(64.7)	(57.6)
Deferred Acquisition Costs at End of Year		63.6	61.1	63.6
Group Life and AD&D | Unum US
Movement Analysis of Deferred Policy Acquisition Costs
Deferred Acquisition Costs at Beginning of Year		51.1	48.9	49.3
Capitalization		45.5	40.6	38.6
Amortization expense		(39.0)	(38.4)	(39.0)
Deferred Acquisition Costs at End of Year		57.6	51.1	48.9
Voluntary Benefits | Unum US
Movement Analysis of Deferred Policy Acquisition Costs
Deferred Acquisition Costs at Beginning of Year		614.3	610.6	601.0
Capitalization		123.3	120.2	115.8
Amortization expense		(114.8)	(116.5)	(106.2)
Deferred Acquisition Costs at End of Year		622.8	614.3	610.6
Individual Disability | Unum US
Movement Analysis of Deferred Policy Acquisition Costs
Deferred Acquisition Costs at Beginning of Year		521.2	497.8	464.4
Capitalization		87.4	83.4	87.4
Amortization expense		(56.7)	(60.0)	(54.0)
Deferred Acquisition Costs at End of Year		451.6	521.2	497.8
Individual Disability | Unum US | Long-term Care and Individual Disability Reinsurance Transaction
Movement Analysis of Deferred Policy Acquisition Costs
Change in Deferred Acquisition Costs	[1]	(100.3)
Dental and Vision | Unum US
Movement Analysis of Deferred Policy Acquisition Costs
Deferred Acquisition Costs at Beginning of Year		12.9	11.3	9.4
Capitalization		14.8	14.5	12.7
Amortization expense		(14.6)	(12.9)	(10.8)
Deferred Acquisition Costs at End of Year		$ 13.1	$ 12.9	$ 11.3

[1] 1Reflects the impacts of DAC written off related to the Fortitude Re reinsurance transaction. See Note 14 for further discussion of the reinsurance transaction.