Long-Duration Insurance Contracts - Account Balances by Guaranteed Minimum Interest Rates (Details) $ in Millions	Mar. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)
Policyholder Account Balance [Line Items]
Policyholders' account balances	$ 5,234.6	$ 5,260.6
Less than 2%
Policyholder Account Balance [Line Items]
Policyholders' account balances	947.4	943.6
Equal to 2% but less than 3%
Policyholder Account Balance [Line Items]
Policyholders' account balances	276.0	280.6
Equal to 3% but less than 4%
Policyholder Account Balance [Line Items]
Policyholders' account balances	654.4	668.2
Equal to 4% but less than 5%
Policyholder Account Balance [Line Items]
Policyholders' account balances	2,705.6	2,706.1
5% or higher
Policyholder Account Balance [Line Items]
Policyholders' account balances	90.9	91.7
Policyholder account balance with a guaranteed minimum crediting rate
Policyholder Account Balance [Line Items]
Policyholders' account balances	$ 4,674.3	$ 4,690.2
Minimum | Equal to 2% but less than 3%
Policyholder Account Balance [Line Items]
Policyholder account balance, guaranteed minimum credit rating	2.00%	2.00%
Minimum | Equal to 3% but less than 4%
Policyholder Account Balance [Line Items]
Policyholder account balance, guaranteed minimum credit rating	3.00%	3.00%
Minimum | Equal to 4% but less than 5%
Policyholder Account Balance [Line Items]
Policyholder account balance, guaranteed minimum credit rating	4.00%	4.00%
Minimum | 5% or higher
Policyholder Account Balance [Line Items]
Policyholder account balance, guaranteed minimum credit rating	5.00%	5.00%
Maximum | Less than 2%
Policyholder Account Balance [Line Items]
Policyholder account balance, guaranteed minimum credit rating	2.00%	2.00%
Maximum | Equal to 2% but less than 3%
Policyholder Account Balance [Line Items]
Policyholder account balance, guaranteed minimum credit rating	3.00%	3.00%
Maximum | Equal to 3% but less than 4%
Policyholder Account Balance [Line Items]
Policyholder account balance, guaranteed minimum credit rating	4.00%	4.00%
Maximum | Equal to 4% but less than 5%
Policyholder Account Balance [Line Items]
Policyholder account balance, guaranteed minimum credit rating	5.00%	5.00%
At Guaranteed Minimum | Less than 2%
Policyholder Account Balance [Line Items]
Policyholders' account balances	$ 95.5	$ 262.5
At Guaranteed Minimum | Equal to 2% but less than 3%
Policyholder Account Balance [Line Items]
Policyholders' account balances	232.8	256.1
At Guaranteed Minimum | Equal to 3% but less than 4%
Policyholder Account Balance [Line Items]
Policyholders' account balances	653.5	667.4
At Guaranteed Minimum | Equal to 4% but less than 5%
Policyholder Account Balance [Line Items]
Policyholders' account balances	2,705.6	2,706.1
At Guaranteed Minimum | 5% or higher
Policyholder Account Balance [Line Items]
Policyholders' account balances	90.9	91.7
At Guaranteed Minimum | Policyholder account balance with a guaranteed minimum crediting rate
Policyholder Account Balance [Line Items]
Policyholders' account balances	3,778.3	3,983.8
1-50 Basis Points Above | Less than 2%
Policyholder Account Balance [Line Items]
Policyholders' account balances	393.9	370.6
1-50 Basis Points Above | Equal to 2% but less than 3%
Policyholder Account Balance [Line Items]
Policyholders' account balances	36.4	19.8
1-50 Basis Points Above | Equal to 3% but less than 4%
Policyholder Account Balance [Line Items]
Policyholders' account balances	0.4	0.4
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	$ 430.7	$ 390.8
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
51-150 Basis Points Above | Less than 2%
Policyholder Account Balance [Line Items]
Policyholders' account balances	$ 329.9	$ 214.4
51-150 Basis Points Above | Equal to 2% but less than 3%
Policyholder Account Balance [Line Items]
Policyholders' account balances	6.8	4.7
51-150 Basis Points Above | Equal to 3% but less than 4%
Policyholder Account Balance [Line Items]
Policyholders' account balances	0.5	0.4
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	$ 337.2	$ 219.5
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
Greater Than 150 Basis Points Above | Less than 2%
Policyholder Account Balance [Line Items]
Policyholders' account balances	$ 128.1	$ 96.1
Greater Than 150 Basis Points Above | Equal to 2% but less than 3%
Policyholder Account Balance [Line Items]
Policyholders' account balances	0.0	0.0
Greater Than 150 Basis Points Above | Equal to 3% but less than 4%
Policyholder Account Balance [Line Items]
Policyholders' account balances	0.0	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	$ 128.1	$ 96.1
Greater Than 150 Basis Points Above | Minimum
Policyholder Account Balance [Line Items]
Policyholder account balance, above guaranteed minimum crediting rate	0.0150	0.0150