Deferred Policy Acquisition Costs (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Deferred Policy Acquisition Cost [Line Items]
Deferred Acquisition Costs	$ 2,602.4	$ 2,464.3	$ 2,560.0		$ 2,272.6
Amortization of Deferred Acquisition Costs	(115.9)	(103.6)
Operating Segments
Deferred Policy Acquisition Cost [Line Items]
Deferred Acquisition Costs	2,602.4	2,464.3	2,560.0	$ 2,427.4
Deferral of Acquisition Costs	157.7	141.8
Amortization of Deferred Acquisition Costs	(115.9)	(103.6)
Deferred Policy Acquisition Cost, Experience Adjustment	0.6	(1.3)
Unum US
Deferred Policy Acquisition Cost [Line Items]
Deferred Acquisition Costs	1,198.3	1,164.3	1,185.1	1,152.9	1,168.7
Deferral of Acquisition Costs	79.0	68.3
Amortization of Deferred Acquisition Costs	(65.8)	(56.9)
Deferred Policy Acquisition Cost, Experience Adjustment	0.0	0.0
Unum US | Group Disability
Deferred Policy Acquisition Cost [Line Items]
Deferred Acquisition Costs	62.5	62.5	61.0	60.9
Deferral of Acquisition Costs	14.6	12.7
Amortization of Deferred Acquisition Costs	(13.1)	(11.1)
Unum US | Group Life and AD&D
Deferred Policy Acquisition Cost [Line Items]
Deferred Acquisition Costs	49.3	53.6	49.3	53.9
Deferral of Acquisition Costs	9.8	9.1
Amortization of Deferred Acquisition Costs	(9.8)	(9.4)
Unum US | Individual Disability
Deferred Policy Acquisition Cost [Line Items]
Deferred Acquisition Costs	472.4	447.0	464.4	441.8
Deferral of Acquisition Costs	21.3	17.5
Amortization of Deferred Acquisition Costs	(13.3)	(12.3)
Unum US | Voluntary Benefits
Deferred Policy Acquisition Cost [Line Items]
Deferred Acquisition Costs	604.2	593.3	601.0	588.6
Deferral of Acquisition Costs	30.3	26.6
Amortization of Deferred Acquisition Costs	(27.1)	(21.9)
Unum US | Dental and Vision
Deferred Policy Acquisition Cost [Line Items]
Deferred Acquisition Costs	9.9	7.9	9.4	7.7
Deferral of Acquisition Costs	3.0	2.4
Amortization of Deferred Acquisition Costs	(2.5)	(2.2)
Unum International
Deferred Policy Acquisition Cost [Line Items]
Deferred Acquisition Costs	39.3	36.5	37.0	36.4	32.0
Deferral of Acquisition Costs	3.5	3.5
Amortization of Deferred Acquisition Costs	(1.8)	(2.1)
Deferred Policy Acquisition Cost, Experience Adjustment	0.6	(1.3)
Colonial Life
Deferred Policy Acquisition Cost [Line Items]
Deferred Acquisition Costs	1,364.8	1,263.5	$ 1,337.9	$ 1,238.1	$ 1,071.9
Deferral of Acquisition Costs	75.2	70.0
Amortization of Deferred Acquisition Costs	(48.3)	(44.6)
Deferred Policy Acquisition Cost, Experience Adjustment	$ 0.0	$ 0.0