Investment Gains and Losses Reported in Consolidated Statements of Income (Detail) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
Fixed Maturity Securities
Gross Gains on Sales		$ 0.1	$ 1.2	$ 1.4	$ 1.8
Gross Losses on Sales	[1]	(7.6)	(14.7)	(9.4)	(60.0)
Impairment Loss	[2]	(3.0)	(8.5)	(11.1)	(160.9)
credit losses		0.0	(10.6)	5.9	(11.6)
Mortgage Loans and Other Invested Assets
Gross Gains on Sales		6.2	7.4	6.2	7.4
Other Investments Gross Realized Losses		0.0	0.4	0.0	0.4
Impairment Loss		0.0	0.0	0.0	3.8
Current Period Provisions		0.8	(0.9)	0.2	(0.5)
Embedded Derivative in Modified Coinsurance Arrangement		0.3	1.0	(2.7)	(0.9)
All Other Derivatives		1.2	2.1	2.7	(3.2)
Foreign Currency Transactions		(1.6)	3.9	(3.0)	6.6
Net Investment Loss		$ (5.2)	$ (17.7)	$ (10.2)	$ (224.5)

[1] 1During the six months ended June 30, 2025, we recognized a $23.5 million net loss on sales of fixed maturity securities related to the Closed Block long-term care and Unum US individual disability reinsurance transaction (2025 Fortitude Re reinsurance transaction) and a $19.1 million loss on sales of fixed maturity securities related to the funding of an extraordinary dividend from a wholly owned insurance subsidiary to Unum Group.

[2] During the three and six months ended June 30, 2025, we recognized impairment losses of $8.5 million and $160.9 million, respectively, based on the intent to dispose of fixed maturity securities with a fair value of $1,250.9 million related to the 2025 Fortitude Re reinsurance transaction.