Mortgage Loans, Allowance for Credit Losses Rollforward (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Financing Receivable, Allowance for Credit Loss, Beginning Balance				$ 15.9
Financing Receivable, Allowance for Credit Loss, Ending Balance		$ 16.0		16.0
Commercial Real Estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Financing Receivable, Allowance for Credit Loss, Beginning Balance	[1]	15.3	$ 16.6	15.9	$ 16.1
Current Period Provisions	[1]	0.7	(1.0)	0.1	(0.5)
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]	16.0	15.6	16.0	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]	4.1	3.8	4.3	4.2
Current Period Provisions	[1]	0.0	0.0	(0.2)	(0.4)
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]	4.1	3.8	4.1	3.8
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]	0.6	1.7	0.7	1.7
Current Period Provisions	[1]	0.2	(0.2)	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]	0.8	1.5	0.8	1.5
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]	1.4	3.1	1.9	2.2
Current Period Provisions	[1]	(0.4)	(2.0)	(0.9)	(1.1)
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]	1.0	1.1	1.0	1.1
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	8.0	9.0	8.0
Current Period Provisions	[1]	0.9	1.2	1.1	1.2
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]	$ 10.1	$ 9.2	$ 10.1	$ 9.2

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