Investment Gains and Losses Reported in Consolidated Statements of Income (Detail) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Fixed Maturity Securities
Gross Gains on Sales		$ 1.2	$ 0.0	$ 1.8	$ 0.0
Gross Losses on Sales	[1]	(14.7)	(5.4)	(60.0)	(21.2)
Impairment Loss	[2]	(8.5)	(1.2)	(160.9)	(1.2)
credit losses		(10.6)	(2.9)	(11.6)	(2.9)
Other Investments
Gross Gains on Sales		7.4	0.0	7.4	0.0
Other Investments Gross Realized Losses		(0.4)	0.0	(0.4)	0.0
Impairment Loss		0.0	0.0	3.8	0.0
Current Period Provisions		(0.9)	1.4	(0.5)	1.9
Embedded Derivative in Modified Coinsurance Arrangement		1.0	0.8	(0.9)	6.9
All Other Derivatives		2.1	0.4	(3.2)	2.0
Foreign Currency Transactions		3.9	(0.7)	6.6	(2.6)
Other Realized Gain		0.0	0.0	0.0	9.3
Net Investment Loss		$ (17.7)	$ (10.4)	$ (224.5)	$ (11.6)

[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 an anticipated 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] 2During 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 related to an anticipated reinsurance transaction.