Mortgage Loans, Allowance for Credit Losses Rollforward (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Financing Receivable, Allowance for Credit Loss, Beginning Balance				$ 16.1
Current Period Provisions		$ 0.0	$ 4.5	(0.5)	$ 6.4
Financing Receivable, Allowance for Credit Loss, Ending Balance		15.6		15.6
Commercial Real Estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Financing Receivable, Allowance for Credit Loss, Beginning Balance	[1]			16.1
Write-offs		(0.8)
Financing Receivable, Allowance for Credit Loss, Ending Balance	[1]	15.6		15.6
Commercial Real Estate | Loan to Value Ratio Below or Equal to 65 Percent
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Financing Receivable, Allowance for Credit Loss, Beginning Balance	[1]	3.8	3.7	4.2	3.8
Current Period Provisions	[1]	0.3	0.3	(0.1)	0.2
Write-offs	[1]	0.0	0.0	0.0	0.0
Recoveries	[1]	0.0	0.0	0.0	0.0
Financing Receivable, Allowance for Credit Loss, Ending Balance	[1]	4.1	4.0	4.1	4.0
Commercial Real Estate | Loan To Value Ratio Above 65 To 75 Percent
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Financing Receivable, Allowance for Credit Loss, Beginning Balance	[1]	1.5	3.3	1.7	3.8
Current Period Provisions	[1]	(0.4)	(1.1)	(0.6)	(1.6)
Write-offs	[1]	0.0	0.0	0.0	0.0
Recoveries	[1]	0.0	0.0	0.0	0.0
Financing Receivable, Allowance for Credit Loss, Ending Balance	[1]	1.1	2.2	1.1	2.2
Commercial Real Estate | Loan To Value Ratio Above 75 To 85 Percent
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Financing Receivable, Allowance for Credit Loss, Beginning Balance	[1]	1.1	1.7	2.2	1.2
Current Period Provisions	[1]	0.9	0.8	(0.2)	1.3
Write-offs	[1]	(0.8)	0.0	(0.8)	0.0
Recoveries	[1]	0.0	0.0	0.0	0.0
Financing Receivable, Allowance for Credit Loss, Ending Balance	[1]	1.2	2.5	1.2	2.5
Commercial Real Estate | Loan To Value Ratio Above 85 Percent
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Financing Receivable, Allowance for Credit Loss, Beginning Balance	[1]	9.2	3.4	8.0	1.4
Current Period Provisions	[1]	0.0	4.4	1.2	6.4
Write-offs	[1]	0.0	0.0	0.0	0.0
Recoveries	[1]	0.0	0.0	0.0	0.0
Financing Receivable, Allowance for Credit Loss, Ending Balance	[1]	9.2	7.8	9.2	7.8
Commercial Real Estate | Loan to Value Ratio Total
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Financing Receivable, Allowance for Credit Loss, Beginning Balance	[1]	15.6	12.1	16.1	10.2
Current Period Provisions	[1]	0.8	4.4	0.3	6.3
Write-offs	[1]	(0.8)	0.0	(0.8)	0.0
Recoveries	[1]	0.0	0.0	0.0	0.0
Financing Receivable, Allowance for Credit Loss, Ending Balance	[1]	$ 15.6	$ 16.5	$ 15.6	$ 16.5

[1] 1Loan-to-Value Ratio utilizes the most recent internal valuation of the property