Mortgage Loans, Allowance for Credit Losses Rollforward (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2020	Jan. 01, 2020
Financing Receivable, Allowance for Credit Loss Rollforward, Mortgage Loans
Current Period Provisions	$ 2.6
Commercial Real Estate
Financing Receivable, Allowance for Credit Loss Rollforward, Mortgage Loans
Financing Receivable, Allowance for Credit Losses, Mortgage Loans	11.1	$ 8.3
Current Period Provisions	2.8
Write-offs	0.0
Recoveries	0.0
Commercial Real Estate \| Loan to Value Ratio Below or Equal to 65 Percent
Financing Receivable, Allowance for Credit Loss Rollforward, Mortgage Loans
Financing Receivable, Allowance for Credit Losses, Mortgage Loans	3.5	2.8
Current Period Provisions	0.7
Write-offs	0.0
Recoveries	0.0
Commercial Real Estate \| Loan To Value Ratio Above 65 To 75 Percent
Financing Receivable, Allowance for Credit Loss Rollforward, Mortgage Loans
Financing Receivable, Allowance for Credit Losses, Mortgage Loans	6.5	4.6
Current Period Provisions	1.9
Write-offs	0.0
Recoveries	0.0
Commercial Real Estate \| Loan To Value Ratio Above 75 To 85 Percent
Financing Receivable, Allowance for Credit Loss Rollforward, Mortgage Loans
Financing Receivable, Allowance for Credit Losses, Mortgage Loans	0.4	0.5
Current Period Provisions	(0.1)
Write-offs	0.0
Recoveries	0.0
Commercial Real Estate \| Loan To Value Ratio Above 85 Percent
Financing Receivable, Allowance for Credit Loss Rollforward, Mortgage Loans
Financing Receivable, Allowance for Credit Losses, Mortgage Loans	0.7	$ 0.4
Current Period Provisions	0.3
Write-offs	0.0
Recoveries	$ 0.0

Amount of allowance for credit loss on financing receivable. Excludes allowance for financing receivable covered under loss sharing agreement.

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Amount of recovery of financing receivables doubtful of collection that were previously charged off.

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Amount of writeoff of financing receivable, charged against allowance for credit loss.

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Amount of credit loss expense (reversal of expense) for financing receivable.

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