Investment Gains and Losses Reported in Consolidated Statements of Income (Detail) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2026	Sep. 30, 2025
Fixed Maturity Securities
Gross Gains on Sales		$ 0.1	$ 139.2	$ 1.5	$ 141.0
Gross Losses on Sales	[1]	(21.3)	(11.5)	(30.7)	(71.5)
Impairment Loss		(760.9)	0.0	(772.0)	(160.9)
credit losses		0.0	(0.8)	5.9	(12.4)
Mortgage Loans and Other Invested Assets
Gross Gains on Sales		0.2	0.2	6.4	7.6
Other Investments Gross Realized Losses		0.0	0.0	0.0	0.4
Impairment Loss		0.0	1.6	0.0	5.4
Current Period Provisions		0.4	0.0	0.5	(0.5)
Embedded Derivative in Modified Coinsurance Arrangement		3.6	3.3	0.9	2.4
All Other Derivatives		(73.5)	0.1	(70.8)	(3.1)
Foreign Currency Transactions		(0.8)	(0.9)	(3.9)	5.7
Net Investment Gain (Loss)		$ (853.0)	$ 128.0	$ (863.2)	$ (96.5)

[1] 1During the three and nine months ended September 30, 2026 we recognized $754.4 million of realized losses based on the intent to dispose of fixed maturity securities with a fair value of $4,232.3 million related to the 2026 reinsurance transaction with Fortitude Reinsurance Company Ltd. (Fortitude Re). Our investment gains and losses on fixed maturity securities for the third quarter and first nine months of 2025 were driven primarily by the Closed Block long-term care and Unum US individual disability reinsurance transaction (2025 Fortitude Re reinsurance transaction) which resulted in a net gain of $137.6 million in the third quarter of 2025 and a net loss of $46.8 million in the first nine months of 2025. We also realized 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 in the first nine months of 2025.