Long-Duration Insurance Contracts - Undiscounted and Discounted Expected Gross Premiums and Expected Future Benefits and Expenses (Details) - USD ($) $ in Millions	Jun. 30, 2023	Dec. 31, 2022
Whole Life
Liability for Future Policy Benefit, by Product Segment [Line Items]
Expected future gross premiums, undiscounted	$ 473.5	$ 469.0
Expected future benefits and expenses, undiscounted	1,134.3	1,121.4
Expected future gross premiums, discounted	325.1	322.5
Expected future benefits and expenses, discounted	588.7	580.4
Term Life
Liability for Future Policy Benefit, by Product Segment [Line Items]
Expected future gross premiums, undiscounted	751.4	739.3
Expected future benefits and expenses, undiscounted	693.9	678.0
Expected future gross premiums, discounted	469.0	464.2
Expected future benefits and expenses, discounted	406.4	401.0
Experience Life
Liability for Future Policy Benefit, by Product Segment [Line Items]
Expected future gross premiums, undiscounted	551.9	569.6
Expected future benefits and expenses, undiscounted	1,728.7	1,755.4
Expected future gross premiums, discounted	306.7	315.5
Expected future benefits and expenses, discounted	799.6	805.2
Limited Pay Whole Life
Liability for Future Policy Benefit, by Product Segment [Line Items]
Expected future gross premiums, undiscounted	63.1	60.8
Expected future benefits and expenses, undiscounted	234.6	226.8
Expected future gross premiums, discounted	48.1	46.5
Expected future benefits and expenses, discounted	102.6	98.6
Supplemental health
Liability for Future Policy Benefit, by Product Segment [Line Items]
Expected future gross premiums, undiscounted	1,645.7	1,640.5
Expected future benefits and expenses, undiscounted	720.7	730.4
Expected future gross premiums, discounted	1,213.6	1,214.9
Expected future benefits and expenses, discounted	525.8	537.0
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	158.1	157.7
Expected future gross premiums, discounted	0.0	0.0
Expected future benefits and expenses, discounted	$ 113.0	$ 113.4