Long-Duration Insurance Contracts - Account Balances by Guaranteed Minimum Interest Rates (Details) $ in Millions	Mar. 31, 2026 USD ($)	Dec. 31, 2025 USD ($)
Policyholder Account Balance [Line Items]
Policyholders' account balances	$ 5,056.1	$ 5,064.1
Less than 2%
Policyholder Account Balance [Line Items]
Policyholders' account balances	$ 718.0	$ 727.1
Less than 2% | Maximum
Policyholder Account Balance [Line Items]
Policyholder account balance, guaranteed minimum credit rating	2.00%	2.00%
Equal to 2% but less than 3%
Policyholder Account Balance [Line Items]
Policyholders' account balances	$ 516.2	$ 498.8
Equal to 2% but less than 3% | Minimum
Policyholder Account Balance [Line Items]
Policyholder account balance, guaranteed minimum credit rating	2.00%	2.00%
Equal to 2% but less than 3% | Maximum
Policyholder Account Balance [Line Items]
Policyholder account balance, guaranteed minimum credit rating	3.00%	3.00%
Equal to 3% but less than 4%
Policyholder Account Balance [Line Items]
Policyholders' account balances	$ 722.6	$ 725.4
Equal to 3% but less than 4% | Minimum
Policyholder Account Balance [Line Items]
Policyholder account balance, guaranteed minimum credit rating	3.00%	3.00%
Equal to 3% but less than 4% | Maximum
Policyholder Account Balance [Line Items]
Policyholder account balance, guaranteed minimum credit rating	4.00%	4.00%
Equal to 4% but less than 5%
Policyholder Account Balance [Line Items]
Policyholders' account balances	$ 2,518.4	$ 2,528.1
Equal to 4% but less than 5% | Minimum
Policyholder Account Balance [Line Items]
Policyholder account balance, guaranteed minimum credit rating	4.00%	4.00%
Equal to 4% but less than 5% | Maximum
Policyholder Account Balance [Line Items]
Policyholder account balance, guaranteed minimum credit rating	5.00%	5.00%
5% or higher
Policyholder Account Balance [Line Items]
Policyholders' account balances	$ 77.1	$ 78.1
5% or higher | Minimum
Policyholder Account Balance [Line Items]
Policyholder account balance, guaranteed minimum credit rating	5.00%	5.00%
Policyholder account balance with a guaranteed minimum crediting rate
Policyholder Account Balance [Line Items]
Policyholders' account balances	$ 4,552.3	$ 4,557.5
At Guaranteed Minimum | Less than 2%
Policyholder Account Balance [Line Items]
Policyholders' account balances	6.8	8.3
At Guaranteed Minimum | Equal to 2% but less than 3%
Policyholder Account Balance [Line Items]
Policyholders' account balances	48.7	63.8
At Guaranteed Minimum | Equal to 3% but less than 4%
Policyholder Account Balance [Line Items]
Policyholders' account balances	574.4	577.6
At Guaranteed Minimum | Equal to 4% but less than 5%
Policyholder Account Balance [Line Items]
Policyholders' account balances	2,518.4	2,528.1
At Guaranteed Minimum | 5% or higher
Policyholder Account Balance [Line Items]
Policyholders' account balances	77.1	78.1
At Guaranteed Minimum | Policyholder account balance with a guaranteed minimum crediting rate
Policyholder Account Balance [Line Items]
Policyholders' account balances	$ 3,225.4	$ 3,255.9
1-50 Basis Points Above | Minimum
Policyholder Account Balance [Line Items]
Policyholder account balance, above guaranteed minimum crediting rate	0.0001	0.0001
1-50 Basis Points Above | Maximum
Policyholder Account Balance [Line Items]
Policyholder account balance, above guaranteed minimum crediting rate	0.0050	0.0050
1-50 Basis Points Above | Less than 2%
Policyholder Account Balance [Line Items]
Policyholders' account balances	$ 6.9	$ 10.0
1-50 Basis Points Above | Equal to 2% but less than 3%
Policyholder Account Balance [Line Items]
Policyholders' account balances	162.3	142.4
1-50 Basis Points Above | Equal to 3% but less than 4%
Policyholder Account Balance [Line Items]
Policyholders' account balances	11.0	10.4
1-50 Basis Points Above | Equal to 4% but less than 5%
Policyholder Account Balance [Line Items]
Policyholders' account balances	0.0	0.0
1-50 Basis Points Above | 5% or higher
Policyholder Account Balance [Line Items]
Policyholders' account balances	0.0	0.0
1-50 Basis Points Above | Policyholder account balance with a guaranteed minimum crediting rate
Policyholder Account Balance [Line Items]
Policyholders' account balances	$ 180.2	$ 162.8
51-150 Basis Points Above | Minimum
Policyholder Account Balance [Line Items]
Policyholder account balance, above guaranteed minimum crediting rate	0.0051	0.0051
51-150 Basis Points Above | Maximum
Policyholder Account Balance [Line Items]
Policyholder account balance, above guaranteed minimum crediting rate	0.0150	0.0150
51-150 Basis Points Above | Less than 2%
Policyholder Account Balance [Line Items]
Policyholders' account balances	$ 223.7	$ 255.2
51-150 Basis Points Above | Equal to 2% but less than 3%
Policyholder Account Balance [Line Items]
Policyholders' account balances	134.1	127.4
51-150 Basis Points Above | Equal to 3% but less than 4%
Policyholder Account Balance [Line Items]
Policyholders' account balances	31.0	31.7
51-150 Basis Points Above | Equal to 4% but less than 5%
Policyholder Account Balance [Line Items]
Policyholders' account balances	0.0	0.0
51-150 Basis Points Above | 5% or higher
Policyholder Account Balance [Line Items]
Policyholders' account balances	0.0	0.0
51-150 Basis Points Above | Policyholder account balance with a guaranteed minimum crediting rate
Policyholder Account Balance [Line Items]
Policyholders' account balances	$ 388.8	$ 414.3
Greater Than 150 Basis Points Above | Minimum
Policyholder Account Balance [Line Items]
Policyholder account balance, above guaranteed minimum crediting rate	0.0150	0.0150
Greater Than 150 Basis Points Above | Less than 2%
Policyholder Account Balance [Line Items]
Policyholders' account balances	$ 480.6	$ 453.6
Greater Than 150 Basis Points Above | Equal to 2% but less than 3%
Policyholder Account Balance [Line Items]
Policyholders' account balances	171.1	165.1
Greater Than 150 Basis Points Above | Equal to 3% but less than 4%
Policyholder Account Balance [Line Items]
Policyholders' account balances	106.2	105.8
Greater Than 150 Basis Points Above | Equal to 4% but less than 5%
Policyholder Account Balance [Line Items]
Policyholders' account balances	0.0	0.0
Greater Than 150 Basis Points Above | 5% or higher
Policyholder Account Balance [Line Items]
Policyholders' account balances	0.0	0.0
Greater Than 150 Basis Points Above | Policyholder account balance with a guaranteed minimum crediting rate
Policyholder Account Balance [Line Items]
Policyholders' account balances	$ 757.9	$ 724.5