Long-Duration Insurance Contracts - Undiscounted and Discounted Expected Gross Premiums and Expected Future Benefits and Expenses (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Whole Life
Liability for Future Policy Benefit, by Product Segment [Line Items]
Expected future gross premiums, undiscounted	$ 478.8	$ 469.0
Expected future benefits and expenses, undiscounted	1,152.8	1,121.4
Expected future gross premiums, discounted	325.0	322.5
Expected future benefits and expenses, discounted	592.1	580.4
Term Life
Liability for Future Policy Benefit, by Product Segment [Line Items]
Expected future gross premiums, undiscounted	689.0	739.3
Expected future benefits and expenses, undiscounted	682.7	678.0
Expected future gross premiums, discounted	449.4	464.2
Expected future benefits and expenses, discounted	405.4	401.0
Experience life
Liability for Future Policy Benefit, by Product Segment [Line Items]
Expected future gross premiums, undiscounted	530.0	569.6
Expected future benefits and expenses, undiscounted	1,703.1	1,755.4
Expected future gross premiums, discounted	296.1	315.5
Expected future benefits and expenses, discounted	797.5	805.2
Limited-pay whole life
Liability for Future Policy Benefit, by Product Segment [Line Items]
Expected future gross premiums, undiscounted	64.7	60.8
Expected future benefits and expenses, undiscounted	244.9	226.8
Expected future gross premiums, discounted	49.1	46.5
Expected future benefits and expenses, discounted	105.6	98.6
Supplemental health
Liability for Future Policy Benefit, by Product Segment [Line Items]
Expected future gross premiums, undiscounted	1,624.1	1,640.5
Expected future benefits and expenses, undiscounted	719.4	730.7
Expected future gross premiums, discounted	1,192.5	1,214.9
Expected future benefits and expenses, discounted	517.9	537.1
SPIA (life contingent)
Liability for Future Policy Benefit, by Product Segment [Line Items]
Expected future gross premiums, undiscounted	0.0	0.0
Expected future benefits and expenses, undiscounted	156.1	157.7
Expected future gross premiums, discounted	0.0	0.0
Expected future benefits and expenses, discounted	$ 111.4	$ 113.4