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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 financing receivable originated more than five years prior to current fiscal year.

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Amount of financing receivable originated four years prior to current fiscal year.

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Amount of financing receivable originated in current fiscal year.

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Amount of financing receivable originated in fiscal year prior to current fiscal year.

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Amount of financing receivable originated three years prior to current fiscal year.

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Amount of financing receivable originated two years prior to current fiscal year.

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The balance represents the amount of loans that are secured by real estate mortgages, offset by the reserve to cover probable credit losses on the loan portfolio.

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Amount, before allowance for credit loss, of financing receivable.

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Mortgage Loans, Sorted by Applicable Credit Quality Indicators (Detail) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Jan. 01, 2020
Mortgage Loans on Real Estate
Financing Receivable, Allowance for Credit Losses, Mortgage Loans	$ 11.5	$ 13.1
Mortgage Loans, Carrying Amount	2,402.2	2,432.1
Commercial Real Estate
Mortgage Loans on Real Estate
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	1,129.8
Financing Receivable, Originated Four Years before Latest Fiscal Year	311.7
Financing Receivable, Originated Three Years before Latest Fiscal Year	390.1
Financing Receivable, Originated Two Years before Latest Fiscal Year	366.9
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	183.6
Financing Receivable, Originated in Current Fiscal Year	31.6
Financing Receivable, before Allowance for Credit Loss	2,413.7	2,445.2
Financing Receivable, Allowance for Credit Losses, Mortgage Loans	11.5
Loan to Value Ratio Below or Equal to 65 Percent
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	1,180.4	1,189.4
Loan to Value Ratio Below or Equal to 65 Percent \| Commercial Real Estate
Mortgage Loans on Real Estate
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	821.9
Financing Receivable, Originated Four Years before Latest Fiscal Year	131.2
Financing Receivable, Originated Three Years before Latest Fiscal Year	90.6
Financing Receivable, Originated Two Years before Latest Fiscal Year	82.3
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	37.2
Financing Receivable, Originated in Current Fiscal Year	20.2
Financing Receivable, before Allowance for Credit Loss	1,183.4
Financing Receivable, Allowance for Credit Losses, Mortgage Loans	3.0	3.4	$ 3.5	$ 2.8
Loan To Value Ratio Above 65 To 75 Percent
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	986.5	1,000.3
Loan To Value Ratio Above 65 To 75 Percent \| Commercial Real Estate
Mortgage Loans on Real Estate
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	161.1
Financing Receivable, Originated Four Years before Latest Fiscal Year	109.2
Financing Receivable, Originated Three Years before Latest Fiscal Year	280.1
Financing Receivable, Originated Two Years before Latest Fiscal Year	284.6
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	146.4
Financing Receivable, Originated in Current Fiscal Year	11.4
Financing Receivable, before Allowance for Credit Loss	992.8
Financing Receivable, Allowance for Credit Losses, Mortgage Loans	6.3	7.3	6.5	4.6
Loan To Value Ratio Above 75 To 85 Percent
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	156.1	155.8
Loan To Value Ratio Above 75 To 85 Percent \| Commercial Real Estate
Mortgage Loans on Real Estate
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	106.4
Financing Receivable, Originated Four Years before Latest Fiscal Year	37.6
Financing Receivable, Originated Three Years before Latest Fiscal Year	13.3
Financing Receivable, Originated Two Years before Latest Fiscal Year	0.0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	0.0
Financing Receivable, Originated in Current Fiscal Year	0.0
Financing Receivable, before Allowance for Credit Loss	157.3
Financing Receivable, Allowance for Credit Losses, Mortgage Loans	1.2	1.3	0.4	0.5
Loan To Value Ratio Above 85 Percent
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	79.2	86.6
Loan To Value Ratio Above 85 Percent \| Commercial Real Estate
Mortgage Loans on Real Estate
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	40.4
Financing Receivable, Originated Four Years before Latest Fiscal Year	33.7
Financing Receivable, Originated Three Years before Latest Fiscal Year	6.1
Financing Receivable, Originated Two Years before Latest Fiscal Year	0.0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	0.0
Financing Receivable, Originated in Current Fiscal Year	0.0
Financing Receivable, before Allowance for Credit Loss	80.2
Financing Receivable, Allowance for Credit Losses, Mortgage Loans	1.0	1.1	$ 0.7	$ 0.4
Originated Five or More Years before Last Fiscal Year
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	1,125.9
Originated Five or More Years before Last Fiscal Year \| Commercial Real Estate
Mortgage Loans on Real Estate
Financing Receivable, Allowance for Credit Losses, Mortgage Loans	3.9
Originated Four Years before Last Fiscal Year
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	310.1
Originated Four Years before Last Fiscal Year \| Commercial Real Estate
Mortgage Loans on Real Estate
Financing Receivable, Allowance for Credit Losses, Mortgage Loans	1.6
Originated Three Years before Last Fiscal Year
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	388.0
Originated Three Years before Last Fiscal Year \| Commercial Real Estate
Mortgage Loans on Real Estate
Financing Receivable, Allowance for Credit Losses, Mortgage Loans	2.1
Originated Two Years before Last Fiscal Year
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	364.5
Originated Two Years before Last Fiscal Year \| Commercial Real Estate
Mortgage Loans on Real Estate
Financing Receivable, Allowance for Credit Losses, Mortgage Loans	2.4
Originated in Fiscal Year before Latest Fiscal Year
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	182.2
Originated in Fiscal Year before Latest Fiscal Year \| Commercial Real Estate
Mortgage Loans on Real Estate
Financing Receivable, Allowance for Credit Losses, Mortgage Loans	1.4
Originated in Current Fiscal Year
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	31.5
Originated in Current Fiscal Year \| Commercial Real Estate
Mortgage Loans on Real Estate
Financing Receivable, Allowance for Credit Losses, Mortgage Loans	0.1
AA Credit Rating
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	3.4	3.5
AA Credit Rating \| Commercial Real Estate
Mortgage Loans on Real Estate
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	3.4
Financing Receivable, Originated Four Years before Latest Fiscal Year	0.0
Financing Receivable, Originated Three Years before Latest Fiscal Year	0.0
Financing Receivable, Originated Two Years before Latest Fiscal Year	0.0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	0.0
Financing Receivable, Originated in Current Fiscal Year	0.0
Financing Receivable, before Allowance for Credit Loss	3.4
A Credit Rating
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	533.7	510.0
A Credit Rating \| Commercial Real Estate
Mortgage Loans on Real Estate
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	376.2
Financing Receivable, Originated Four Years before Latest Fiscal Year	60.3
Financing Receivable, Originated Three Years before Latest Fiscal Year	63.8
Financing Receivable, Originated Two Years before Latest Fiscal Year	16.7
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	17.9
Financing Receivable, Originated in Current Fiscal Year	0.0
Financing Receivable, before Allowance for Credit Loss	534.9
BBB Credit Rating
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	1,810.0	1,863.0
BBB Credit Rating \| Commercial Real Estate
Mortgage Loans on Real Estate
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	705.0
Financing Receivable, Originated Four Years before Latest Fiscal Year	241.0
Financing Receivable, Originated Three Years before Latest Fiscal Year	326.3
Financing Receivable, Originated Two Years before Latest Fiscal Year	350.2
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	165.7
Financing Receivable, Originated in Current Fiscal Year	31.6
Financing Receivable, before Allowance for Credit Loss	1,819.8
BB Credit Rating
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	39.1	39.4
BB Credit Rating \| Commercial Real Estate
Mortgage Loans on Real Estate
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	29.2
Financing Receivable, Originated Four Years before Latest Fiscal Year	10.4
Financing Receivable, Originated Three Years before Latest Fiscal Year	0.0
Financing Receivable, Originated Two Years before Latest Fiscal Year	0.0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	0.0
Financing Receivable, Originated in Current Fiscal Year	0.0
Financing Receivable, before Allowance for Credit Loss	39.6
B Credit Rating
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	16.0	$ 16.2
B Credit Rating \| Commercial Real Estate
Mortgage Loans on Real Estate
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	16.0
Financing Receivable, Originated Four Years before Latest Fiscal Year	0.0
Financing Receivable, Originated Three Years before Latest Fiscal Year	0.0
Financing Receivable, Originated Two Years before Latest Fiscal Year	0.0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	0.0
Financing Receivable, Originated in Current Fiscal Year	0.0
Financing Receivable, before Allowance for Credit Loss	$ 16.0