Mortgage Loans, Allowance for Credit Losses Rollforward (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended		12 Months Ended
		Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2026	Sep. 30, 2025	Dec. 31, 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		$ 16.4		16.4		$ 15.9
Mortgage Loans (net of allowance for credit losses of $16.4; $15.9)	[1]	2,053.2		2,053.2		2,109.5
Other Investments Gross Realized Losses		0.0	$ 0.0	0.0	$ 0.4
Financial Asset, Past Due
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Mortgage Loans (net of allowance for credit losses of $16.4; $15.9)			8.4		8.4
Loan to Value Ratio Below or Equal to 65 Percent
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Mortgage Loans (net of allowance for credit losses of $16.4; $15.9)	[1]	1,661.8		1,661.8		1,701.2
Loan To Value Ratio Above 65 To 75 Percent
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Mortgage Loans (net of allowance for credit losses of $16.4; $15.9)	[1]	216.2		216.2		164.3
Loan To Value Ratio Above 75 To 85 Percent
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Mortgage Loans (net of allowance for credit losses of $16.4; $15.9)	[1]	122.4		122.4		162.6
Loan To Value Ratio Above 85 Percent
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Mortgage Loans (net of allowance for credit losses of $16.4; $15.9)	[1]	52.8		52.8		81.4
Commercial Real Estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Financing Receivable, Allowance for Credit Loss, Beginning Balance	[2]	16.0	15.6	15.9	16.1	16.1
Current Period Provisions	[2]	0.4	0.8	0.5	0.3
Write-offs	[2]	0.0	(0.8)	0.0	(0.8)
Recoveries	[2]	0.0	0.0	0.0	0.0
Financing Receivable, Allowance for Credit Loss, Ending Balance	[2]	16.4	15.6	16.4	15.6	15.9
Other Investments Gross Realized Losses						1.1
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	[2]	4.1	3.8	4.3	4.2	4.2
Current Period Provisions	[2]	0.2	0.3	0.0	(0.1)
Write-offs	[2]	0.0	0.0	0.0	0.0
Recoveries	[2]	0.0	0.0	0.0	0.0
Financing Receivable, Allowance for Credit Loss, Ending Balance	[2]	4.3	4.1	4.3	4.1	4.3
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	[2]	0.8	1.5	0.7	1.7	1.7
Current Period Provisions	[2]	0.3	(0.4)	0.4	(0.6)
Write-offs	[2]	0.0	0.0	0.0	0.0
Recoveries	[2]	0.0	0.0	0.0	0.0
Financing Receivable, Allowance for Credit Loss, Ending Balance	[2]	1.1	1.1	1.1	1.1	0.7
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	[2]	1.0	1.1	1.9	2.2	2.2
Current Period Provisions	[2]	0.8	0.9	(0.1)	(0.2)
Write-offs	[2]	0.0	(0.8)	0.0	(0.8)
Recoveries	[2]	0.0	0.0	0.0	0.0
Financing Receivable, Allowance for Credit Loss, Ending Balance	[2]	1.8	1.2	1.8	1.2	1.9
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	[2]	10.1	9.2	9.0	8.0	8.0
Current Period Provisions	[2]	(0.9)	0.0	0.2	1.2
Write-offs	[2]	0.0	0.0	0.0	0.0
Recoveries	[2]	0.0	0.0	0.0	0.0
Financing Receivable, Allowance for Credit Loss, Ending Balance	[2]	$ 9.2	$ 9.2	$ 9.2	$ 9.2	$ 9.0

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

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