Policyholder Account Balance (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2026		Mar. 31, 2025		Dec. 31, 2025
Policyholder Account Balance [Roll Forward]
Policyholders' Account Balances	$ 5,736.0				$ 5,636.4
Operating Segments
Policyholder Account Balance [Roll Forward]
Balance, beginning of year	5,467.0		$ 5,470.0
Premiums received	34.7		40.2
Policy Charges	(59.2)	[1]	(59.9)	[2]
Surrenders and withdrawals	(25.2)		(23.2)
Benefit payments	(57.8)		(69.2)
Interest credited	96.9		95.6
Other	2.2		2.5
Balance, end of period	5,458.6		5,456.0
Reserves in excess of account balance	170.9		164.8
Total policyholders' account balances, after reserves in excess of account balance	5,629.5		5,620.8
Policyholder Account Balance, Reinsurance recoverable	4,115.5		4,086.8
Net policyholders' account balances, after reinsurance recoverable	$ 1,514.0		$ 1,534.0
Weighted average crediting rate	7.30%		7.20%
Net Amount at Risk	$ 12,790.1	[3]	$ 13,800.0	[4]
Cash surrender value	5,397.3		5,393.0
Policyholders' Account Balances	5,736.0
Unum US
Policyholder Account Balance [Roll Forward]
Policyholders' Account Balances	659.0
Colonial Life
Policyholder Account Balance [Roll Forward]
Balance, beginning of year	845.2		849.0
Premiums received	18.3		19.4
Policy Charges	(17.1)	[1]	(17.6)	[2]
Surrenders and withdrawals	(10.0)		(10.0)
Benefit payments	(2.2)		(2.2)
Interest credited	8.4		8.5
Other	(0.3)		(0.1)
Balance, end of period	842.3		847.0
Reserves in excess of account balance	13.4		13.8
Policyholder Account Balance, Reinsurance recoverable	0.0		0.1
Net policyholders' account balances, after reinsurance recoverable	$ 855.7		$ 860.7
Weighted average crediting rate	4.10%		4.10%
Net Amount at Risk	$ 7,546.5	[3]	$ 8,057.8	[4]
Cash surrender value	824.1		821.1
Policyholders' Account Balances	855.7		860.8
Closed Block
Policyholder Account Balance [Roll Forward]
Policyholders' Account Balances	4,114.8
Funding Agreements
Policyholder Account Balance [Roll Forward]
Policyholders' Account Balances	106.5
Voluntary Benefits | Unum US
Policyholder Account Balance [Roll Forward]
Balance, beginning of year	548.4		568.8
Premiums received	11.4		12.9
Policy Charges	(13.1)	[1]	(13.9)	[2]
Surrenders and withdrawals	(11.6)		(8.9)
Benefit payments	(1.4)		(1.6)
Interest credited	4.8		5.1
Other	1.7		2.5
Balance, end of period	540.2		564.9
Reserves in excess of account balance	118.8		109.2
Policyholder Account Balance, Reinsurance recoverable	0.7		0.8
Net policyholders' account balances, after reinsurance recoverable	$ 658.3		$ 673.3
Weighted average crediting rate	3.60%		3.70%
Net Amount at Risk	$ 3,635.6	[3]	$ 4,040.4	[4]
Cash surrender value	530.7		554.9
Policyholders' Account Balances	659.0		674.1
Other Insurance Product Line | Closed Block
Policyholder Account Balance [Roll Forward]
Balance, beginning of year	4,073.4		4,052.2
Premiums received	5.0		7.9
Policy Charges	(29.0)	[1]	(28.4)	[2]
Surrenders and withdrawals	(3.6)		(4.3)
Benefit payments	(54.2)		(65.4)
Interest credited	83.7		82.0
Other	0.8		0.1
Balance, end of period	4,076.1		4,044.1
Reserves in excess of account balance	38.7		41.8
Policyholder Account Balance, Reinsurance recoverable	4,114.8		4,085.9
Net policyholders' account balances, after reinsurance recoverable	$ 0.0		$ 0.0
Weighted average crediting rate	8.60%		8.40%
Net Amount at Risk	$ 1,608.0	[3]	$ 1,701.8	[4]
Cash surrender value	4,042.5		4,017.0
Policyholders' Account Balances	$ 4,114.8		$ 4,085.9

[1] 1Contracts included in the policyholders' account balances are generally charged a premium and/or monthly assessments on the basis of the account balance.

[2] 1Contracts included in the policyholders' account balances are generally charged a premium and/or monthly assessments on the basis of the account balance.

[3] 2For those guarantees of benefits that are payable in the event of death, the net amount at risk is generally defined as the current guaranteed minimum death benefit in excess of the current account balance at the balance sheet date.

[4] 2For those guarantees of benefits that are payable in the event of death, the net amount at risk is generally defined as the current guaranteed minimum death benefit in excess of the current account balance at the balance sheet date.