Long-Duration Insurance Contracts - Account Balances by Guaranteed Minimum Interest Rates (Details) $ in Millions	Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)
Policyholder Account Balance [Line Items]
Policyholders' account balances	$ 5,100.3	$ 5,187.0
Less than 2%
Policyholder Account Balance [Line Items]
Policyholders' account balances	$ 797.6	$ 886.1
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	$ 449.4	$ 382.7
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	$ 653.4	$ 609.0
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	$ 2,600.0	$ 2,670.5
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	$ 81.8	$ 86.9
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	$ 4,582.2	$ 4,635.2
At Guaranteed Minimum | Less than 2%
Policyholder Account Balance [Line Items]
Policyholders' account balances	15.9	36.7
At Guaranteed Minimum | Equal to 2% but less than 3%
Policyholder Account Balance [Line Items]
Policyholders' account balances	94.5	162.9
At Guaranteed Minimum | Equal to 3% but less than 4%
Policyholder Account Balance [Line Items]
Policyholders' account balances	545.6	571.3
At Guaranteed Minimum | Equal to 4% but less than 5%
Policyholder Account Balance [Line Items]
Policyholders' account balances	2,600.0	2,670.5
At Guaranteed Minimum | 5% or higher
Policyholder Account Balance [Line Items]
Policyholders' account balances	81.8	86.9
At Guaranteed Minimum | Policyholder account balance with a guaranteed minimum crediting rate
Policyholder Account Balance [Line Items]
Policyholders' account balances	$ 3,337.8	$ 3,528.3
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	$ 77.3	$ 159.8
1-50 Basis Points Above | Equal to 2% but less than 3%
Policyholder Account Balance [Line Items]
Policyholders' account balances	122.2	77.9
1-50 Basis Points Above | Equal to 3% but less than 4%
Policyholder Account Balance [Line Items]
Policyholders' account balances	43.3	36.9
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	$ 242.8	$ 274.6
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	$ 400.4	$ 489.4
51-150 Basis Points Above | Equal to 2% but less than 3%
Policyholder Account Balance [Line Items]
Policyholders' account balances	97.9	65.8
51-150 Basis Points Above | Equal to 3% but less than 4%
Policyholder Account Balance [Line Items]
Policyholders' account balances	13.3	0.7
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	$ 511.6	$ 555.9
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	$ 304.0	$ 200.2
Greater Than 150 Basis Points Above | Equal to 2% but less than 3%
Policyholder Account Balance [Line Items]
Policyholders' account balances	134.8	76.1
Greater Than 150 Basis Points Above | Equal to 3% but less than 4%
Policyholder Account Balance [Line Items]
Policyholders' account balances	51.2	0.0
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	$ 490.0	$ 276.3