Investment Gains and Losses Reported in Consolidated Statements of Income (Detail) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2026	Mar. 31, 2025
Fixed Maturity Securities
Gross Gains on Sales		$ 1.3	$ 0.6
Gross Losses on sales	[1]	(1.8)	(45.3)
Impairment Loss, Debt Securities, Available-for-sale	[2]	(8.1)	(152.4)
Credit Losses		5.9	(1.0)
Mortgage Loans and Other Invested Assets
Impairment Loss, Mortgage Loans and Other Invested Assets		0.0	(3.8)
Credit Losses		0.6	(0.4)
Embedded Derivative in Modified Coinsurance Arrangement		(3.0)	(1.9)
All Other Derivatives		1.5	(5.3)
Foreign Currency Transactions		(1.4)	2.7
Net Investment Loss		$ (5.0)	(206.8)
Commercial Real Estate
Schedule of Investments
Financing Receivable, Modified in Period, Amount			$ 14.2

[1] 1During the three months ended March 31, 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 (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] 2 During the three months ended March 31, 2025, we recognized a $152.4 million impairment loss based on the intent to dispose of fixed maturity securities with a fair value of $1,250.9 million related to the Fortitude Re reinsurance transaction.