Segment Information - Schedule of Financial Information by Segment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Segment Reporting Information [Line Items]
Net premiums and contract charges earned	$ 1,228.4	$ 1,146.0	$ 1,057.1
Net investment income	474.5	445.7	444.8
Other segment income	21.7	20.8	14.0
Total segment revenues	1,724.6	1,612.5	1,515.9
Benefits and claims expenses (excluding catastrophe losses)	583.3	560.2	604.5
Catastrophe losses	61.7	94.9	97.6
Loss adjustment expenses	68.3	72.8	71.5
Interest credited	216.9	215.9	205.7
Operating & admin expenses	334.4	294.9	267.0
Commissions expense	159.4	142.2	130.4
Taxes, licenses and fees	31.1	30.6	27.7
Deferred policy acquisition costs	(135.4)	(122.2)	(107.0)
Deferred policy acquisition cost amortization	124.5	111.1	101.2
Interest expense	36.4	34.6	29.7
Total segment expenses	1,480.6	1,435.0	1,428.3
Pretax profit (loss)	244.0	177.5	87.6
Income tax expense	48.2	36.2	15.6
Segment profit (loss) (Core earnings)	195.8	141.3	72.0
Net investment losses (after-tax)	(10.2)	(13.6)	(18.8)
Non-core income adjustments (after-tax)	(23.5)	(24.9)	(8.2)
Net income	162.1	102.8	45.0
Property & Casualty
Segment Reporting Information [Line Items]
Net premiums and contract charges earned	802.6	736.5	645.6
Net investment income	57.1	46.0	37.9
Other segment income	3.2	2.3	2.8
Total segment revenues	862.9	784.8	686.3
Benefits and claims expenses (excluding catastrophe losses)	366.0	353.3	387.9
Catastrophe losses	61.7	94.9	97.6
Loss adjustment expenses	68.3	72.8	71.5
Interest credited	0.0	0.0	0.0
Operating & admin expenses	136.3	122.4	109.2
Commissions expense	72.0	63.0	52.6
Taxes, licenses and fees	21.2	20.2	17.7
Deferred policy acquisition costs	(103.7)	(89.8)	(76.2)
Deferred policy acquisition cost amortization	98.2	84.6	71.3
Interest expense	0.0	0.0	0.0
Total segment expenses	720.0	721.4	731.6
Pretax profit (loss)	142.9	63.4	(45.3)
Income tax expense	30.5	14.3	(9.8)
Segment profit (loss) (Core earnings)	112.4	49.1	(35.5)
Net investment losses (after-tax)	0.0	0.0	0.0
Non-core income adjustments (after-tax)	0.0	0.0	0.0
Net income	112.4	49.1	(35.5)
Life & Retirement
Segment Reporting Information [Line Items]
Net premiums and contract charges earned	158.6	154.6	151.7
Net investment income	373.2	363.6	369.9
Other segment income	21.2	20.2	17.0
Total segment revenues	553.0	538.4	538.6
Benefits and claims expenses (excluding catastrophe losses)	124.2	128.1	127.7
Catastrophe losses	0.0	0.0	0.0
Loss adjustment expenses	0.0	0.0	0.0
Interest credited	211.6	211.2	201.8
Operating & admin expenses	99.6	93.2	83.9
Commissions expense	42.3	41.1	37.2
Taxes, licenses and fees	4.0	3.8	3.9
Deferred policy acquisition costs	(26.6)	(28.3)	(26.2)
Deferred policy acquisition cost amortization	24.3	24.6	28.0
Interest expense	0.0	0.0	0.0
Total segment expenses	479.4	473.7	456.3
Pretax profit (loss)	73.6	64.7	82.3
Income tax expense	12.6	10.5	14.1
Segment profit (loss) (Core earnings)	61.0	54.2	68.2
Net investment losses (after-tax)	0.0	0.0	0.0
Non-core income adjustments (after-tax)	(4.2)	2.1	3.3
Net income	56.8	56.3	71.5
Supplemental & Group Benefits
Segment Reporting Information [Line Items]
Net premiums and contract charges earned	267.2	254.9	259.8
Net investment income	40.3	38.1	38.9
Other segment income	(5.1)	(4.6)	(11.1)
Total segment revenues	302.4	288.4	287.6
Benefits and claims expenses (excluding catastrophe losses)	93.1	78.8	88.9
Catastrophe losses	0.0	0.0	0.0
Loss adjustment expenses	0.0	0.0	0.0
Interest credited	5.3	4.7	3.9
Operating & admin expenses	81.7	70.7	66.9
Commissions expense	45.1	38.1	40.6
Taxes, licenses and fees	5.3	5.9	5.7
Deferred policy acquisition costs	(5.1)	(4.1)	(4.6)
Deferred policy acquisition cost amortization	2.0	1.9	1.9
Interest expense	0.0	0.0	0.0
Total segment expenses	227.4	196.0	203.3
Pretax profit (loss)	75.0	92.4	84.3
Income tax expense	16.3	20.7	17.9
Segment profit (loss) (Core earnings)	58.7	71.7	66.4
Net investment losses (after-tax)	0.0	0.0	0.0
Non-core income adjustments (after-tax)	(13.7)	(11.3)	(11.5)
Net income	45.0	60.4	54.9
Corporate & Other
Segment Reporting Information [Line Items]
Net premiums and contract charges earned	0.0	0.0	0.0
Net investment income	3.9	(2.0)	(1.9)
Other segment income	2.4	2.9	5.3
Total segment revenues	6.3	0.9	3.4
Benefits and claims expenses (excluding catastrophe losses)	0.0	0.0	0.0
Catastrophe losses	0.0	0.0	0.0
Loss adjustment expenses	0.0	0.0	0.0
Interest credited	0.0	0.0	0.0
Operating & admin expenses	16.8	8.6	7.0
Commissions expense	0.0	0.0	0.0
Taxes, licenses and fees	0.6	0.7	0.4
Deferred policy acquisition costs	0.0	0.0	0.0
Deferred policy acquisition cost amortization	0.0	0.0	0.0
Interest expense	36.4	34.6	29.7
Total segment expenses	53.8	43.9	37.1
Pretax profit (loss)	(47.5)	(43.0)	(33.7)
Income tax expense	(11.2)	(9.3)	(6.6)
Segment profit (loss) (Core earnings)	(36.3)	(33.7)	(27.1)
Net investment losses (after-tax)	(10.2)	(13.6)	(18.8)
Non-core income adjustments (after-tax)	(5.6)	(15.7)	0.0
Net income	$ (52.1)	$ (63.0)	$ (45.9)