Investments - Mortgage Loan Credit Monitoring (Details) - USD ($) $ in Millions	6 Months Ended
Jun. 30, 2025	Dec. 31, 2024
Vintage year, Direct financing leases
2025	$ 42.1
2024	10.2	$ 48.3
2023	1.9	1.8
2022	124.3	126.3
2021	47.0	43.7
2020		90.0
Prior (prior period)		252.9
Prior (current period)	339.9
Direct financing leases, Total amortized cost	565.4	563.0
Reinsurance recoverable and deposit receivable	19,339.1	19,493.4
Accrued interest receivable on direct financing leases	1.3	1.2
Mortgage and other loans
Accrued interest receivable	464.9	647.3
A- and above
Vintage year, Direct financing leases
2024		1.0
2022	32.0	38.5
2021	11.4	11.0
2020		33.8
Prior (prior period)		177.4
Prior (current period)	213.2
Direct financing leases, Total amortized cost	256.6	261.7
BBB+ thru BBB-
Vintage year, Direct financing leases
2024	10.2	4.9
2023		1.8
2022	91.7	87.3
2021	21.0	19.0
2020		52.8
Prior (prior period)		67.0
Prior (current period)	95.4
Direct financing leases, Total amortized cost	218.3	232.8
BB+ thru BB-
Vintage year, Direct financing leases
2025	42.1
2024		38.8
2023	1.9
2022	0.6	0.5
2021	7.1	6.8
2020		3.4
Prior (prior period)		8.5
Prior (current period)	31.3
Direct financing leases, Total amortized cost	83.0	58.0
B+ and below
Vintage year, Mortgage loans
2024		3.6
2021		6.9
Mortgage loans, Total amortized cost		10.5
Vintage year, Direct financing leases
2021	7.5
Direct financing leases, Total amortized cost	7.5
Commercial mortgage loans
Vintage year, Mortgage loans
2025	791.4
2024	1,557.4	1,607.8
2023	1,402.6	1,330.1
2022	1,506.6	1,620.2
2021	2,201.8	2,418.3
2020		1,686.6
Prior (current period)	9,369.5
Prior (prior period)		8,409.7
Mortgage loans, Total amortized cost	16,829.3	17,072.7
Mortgage and other loans
Accrued interest receivable	73.1	69.2
Commercial mortgage loans \| A- and above
Vintage year, Mortgage loans
2025	688.4
2024	1,281.1	1,182.1
2023	873.9	793.1
2022	1,135.4	1,234.3
2021	2,025.4	2,101.3
2020		1,463.4
Prior (current period)	7,425.7
Prior (prior period)		6,594.0
Mortgage loans, Total amortized cost	13,429.9	13,368.2
Commercial mortgage loans \| BBB+ thru BBB-
Vintage year, Mortgage loans
2025	33.5
2024	159.7	210.0
2023	385.0	393.6
2022	214.5	231.6
2021	127.9	269.1
2020		180.6
Prior (current period)	1,411.4
Prior (prior period)		1,217.5
Mortgage loans, Total amortized cost	2,332.0	2,502.4
Commercial mortgage loans \| BB+ thru BB-
Vintage year, Mortgage loans
2025	41.3
2024	116.6	215.7
2023	143.7	143.4
2022	156.7	154.3
2021	48.5	47.9
2020		40.1
Prior (current period)	164.9
Prior (prior period)		271.7
Mortgage loans, Total amortized cost	671.7	873.1
Commercial mortgage loans \| B+ and below
Vintage year, Mortgage loans
2025	28.2
2020		2.5
Prior (current period)	367.5
Prior (prior period)		326.5
Mortgage loans, Total amortized cost	395.7	329.0
Residential mortgage loans
Vintage year, Mortgage loans
2025 mortgage loans excluding portfolio layer method basis adjustments	449.4
2024 mortgage loans excluding portfolio layer method basis adjustments	438.1	350.9
2023 mortgage loans excluding portfolio layer method basis adjustments	403.4	417.0
2022 mortgage loans excluding portfolio layer method basis adjustments	960.8	976.4
2021 mortgage loans excluding portfolio layer method basis adjustments	1,191.7	1,239.7
2020 mortgage loans excluding portfolio layer method basis adjustments		198.5
Prior mortgage loans excluding portfolio layer method basis adjustments (prior period)		433.3
Prior mortgage loans excluding portfolio layer method basis adjustments (current period)	603.0
Total mortgage loans excluding portfolio layer method basis adjustments	4,046.4	3,615.8
Unallocated portfolio layer method basis adjustment	(1.5)	(8.4)
Mortgage loans, Total amortized cost	4,044.9	3,607.4
Mortgage and other loans
Accrued interest receivable	15.4	12.0
Residential mortgage loans \| Performing
Vintage year, Mortgage loans
2025	449.4
2024	438.0	350.4
2023	397.2	411.5
2022	954.1	970.3
2021	1,186.4	1,234.9
2020		196.0
Prior (current period)	598.1
Prior (prior period)		427.6
Mortgage loans, Total amortized cost	4,023.2	3,590.7
Residential mortgage loans \| Non-performing
Vintage year, Mortgage loans
2024	0.1	0.5
2023	6.2	5.5
2022	6.7	6.1
2021	5.3	4.8
2020		2.5
Prior (current period)	4.9
Prior (prior period)		5.7
Mortgage loans, Total amortized cost	$ 23.2	25.1
Mortgage and other loans
Mortgage loans, delinquent to be considered non-performing (in days)	90 days
Other loans
Vintage year, Mortgage loans
2025	$ 40.8
2024	49.7	84.3
2023	44.9	61.9
Prior (prior period)		0.1
Mortgage loans, Total amortized cost	135.4	146.3
Mortgage and other loans
Accrued interest receivable	1.0	1.3
Other loans \| Performing
Vintage year, Mortgage loans
2025	40.8
2024	47.8	84.2
2023	43.8	61.9
Mortgage loans, Total amortized cost	132.4	146.1
Other loans \| Non-performing
Vintage year, Mortgage loans
2024	1.9	0.1
2023	1.1
Prior (prior period)		0.1
Mortgage loans, Total amortized cost	$ 3.0	$ 0.2

The numbers of days for which a mortgage loan has been delinquent such that it is considered non-performing.

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- Definition

Carrying amount as of the balance sheet date of interest earned but not received on direct financing lease. Also called accrued interest or accrued interest receivable.

+ References

No definition available.

+ Details

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Amount of net investment in direct financing lease originated five years prior to current fiscal year.

+ References

No definition available.

+ Details

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- Definition

Amount of net investment in direct financing lease originated six or more years prior to current fiscal year.

+ References

No definition available.

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- Definition

Amortized cost excluding accrued interest, before allowance for credit loss, of financing receivable before portfolio layer method adjustment. Excludes net investment in lease.

+ References

No definition available.

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Amortized cost excluding accrued interest, before allowance for credit loss, of financing receivable of portfolio layer method adjustment. Excludes net investment in lease.

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No definition available.

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Amortized cost excluding accrued interest, of financing receivable before portfolio layer method basis adjustment originated more than five years prior to current fiscal year. Excludes net investment in lease.

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Amortized cost excluding accrued interest, of financing receivable before portfolio layer method basis adjustment originated more than six years prior to current fiscal year. Excludes net investment in lease.

+ References

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Amortized cost excluding accrued interest, of financing receivable before portfolio layer method basis adjustment originated in current fiscal year. Excludes net investment in lease.

+ References

No definition available.

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Amortized cost excluding accrued interest, of financing receivable originated more than six years prior to current fiscal year. Excludes net investment in lease.

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Amortized cost excluding accrued interest of financing receivable before portfolio layer method basis adjustment originated four years prior to current fiscal year. Excludes net investment in lease.

+ References

No definition available.

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Amortized cost excluding accrued interest of financing receivable before portfolio layer method basis adjustment originated three years prior to current fiscal year. Excludes net investment in lease.

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No definition available.

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Amortized cost excluding accrued interest of financing receivable before portfolio layer method basis adjustment originated five years prior to current fiscal year. Excludes net investment in lease.

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Amortized cost excluding accrued interest of financing receivable originated five years prior to current fiscal year. Excludes net investment in lease.

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Amortized cost excluding accrued interest of financing receivable before portfolio layer method basis adjustment originated two years prior to current fiscal year. Excludes net investment in lease.

+ References

No definition available.

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Amortized cost excluding accrued interest of financing receivable before portfolio layer method basis adjustment originated in fiscal year prior to current fiscal year. Excludes net investment in lease.

+ References

No definition available.

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- References

No definition available.

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Amount excluding accrued interest, before allowance for credit loss, of net investment in direct financing lease.

+ References

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Amount of net investment in direct financing lease originated more than five years prior to current fiscal year.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-6

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Amount of net investment in direct financing lease originated four years prior to current fiscal year.

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Amount of net investment in direct financing lease originated in current fiscal year.

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Amount of net investment in direct financing lease originated in fiscal year prior to current fiscal year.

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Amount of net investment in direct financing lease originated three years prior to current fiscal year.

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Amount of net investment in direct financing lease originated two years prior to current fiscal year.

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Amortized cost excluding accrued interest, before allowance for credit loss, of financing receivable. Excludes net investment in lease.

+ References

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Amortized cost excluding accrued interest, of financing receivable originated more than five years prior to current fiscal year. Excludes net investment in lease.

+ References

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Amortized cost excluding accrued interest, of financing receivable originated four years prior to current fiscal year. Excludes net investment in lease.

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Amortized cost excluding accrued interest, of financing receivable originated three years prior to current fiscal year. Excludes net investment in lease.

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Amortized cost excluding accrued interest, of financing receivable originated in current fiscal year. Excludes net investment in lease.

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Amortized cost excluding accrued interest, of financing receivable originated two years prior to current fiscal year. Excludes net investment in lease.

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Amortized cost excluding accrued interest of financing receivable originated in fiscal year prior to current fiscal year. Excludes net investment in lease.

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Carrying amount as of the balance sheet date of interest earned but not received. Also called accrued interest or accrued interest receivable.

+ References

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Amount before valuation allowance recoverable under reinsurance contracts. Examples include, but are not limited to, settled and unsettled claims, incurred but not reported losses, loss adjustment expense, premium paid, policy benefits and policy reserves.

+ References

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