Long-Duration Insurance Contracts - Undiscounted and Discounted Expected Gross Premiums and Expected Future Benefits and Expenses (Details) - USD ($) $ in Millions	Mar. 31, 2023	Mar. 31, 2022
Whole Life
Liability for Future Policy Benefit, by Product Segment [Line Items]
Expected future gross premiums, undiscounted	$ 471.6	$ 448.0
Expected future benefits and expenses, undiscounted	1,128.1	1,080.6
Expected future gross premiums, discounted	322.5	308.9
Expected future benefits and expenses, discounted	585.4	568.1
Term Life
Liability for Future Policy Benefit, by Product Segment [Line Items]
Expected future gross premiums, undiscounted	744.6	720.9
Expected future benefits and expenses, undiscounted	687.8	597.0
Expected future gross premiums, discounted	465.3	447.0
Expected future benefits and expenses, discounted	405.2	355.8
Experience Life
Liability for Future Policy Benefit, by Product Segment [Line Items]
Expected future gross premiums, undiscounted	559.0	598.4
Expected future benefits and expenses, undiscounted	1,740.3	1,774.5
Expected future gross premiums, discounted	310.2	329.4
Expected future benefits and expenses, discounted	801.5	799.5
Limited Pay Whole Life
Liability for Future Policy Benefit, by Product Segment [Line Items]
Expected future gross premiums, undiscounted	61.9	51.3
Expected future benefits and expenses, undiscounted	230.7	196.9
Expected future gross premiums, discounted	47.3	39.7
Expected future benefits and expenses, discounted	100.3	88.8
Supplemental health
Liability for Future Policy Benefit, by Product Segment [Line Items]
Expected future gross premiums, undiscounted	1,644.2	1,633.3
Expected future benefits and expenses, undiscounted	724.6	776.3
Expected future gross premiums, discounted	1,215.1	127.3
Expected future benefits and expenses, discounted	530.6	577.4
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	158.2	161.6
Expected future gross premiums, discounted	0.0	0.0
Expected future benefits and expenses, discounted	$ 113.3	$ 116.2