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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, 2022	Dec. 31, 2021	Mar. 31, 2021	Dec. 31, 2020
Mortgage Loans on Real Estate
Financing Receivable, Allowance for Credit Losses, Mortgage Loans	$ 7.9	$ 8.3
Mortgage Loans, Carrying Amount	2,529.5	2,560.4
Commercial Real Estate
Mortgage Loans on Real Estate
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	1,230.8	984.1
Financing Receivable, Originated Four Years before Latest Fiscal Year	382.4	305.5
Financing Receivable, Originated Three Years before Latest Fiscal Year	358.7	384.4
Financing Receivable, Originated Two Years before Latest Fiscal Year	179.6	360.8
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	351.7	180.7
Financing Receivable, Originated in Current Fiscal Year	34.2	353.2
Financing Receivable, before Allowance for Credit Loss	2,537.4	2,568.7
Financing Receivable, Allowance for Credit Losses, Mortgage Loans	7.9	8.3
Loan to Value Ratio Below or Equal to 65 Percent
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	1,322.4	1,346.1
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	887.9	779.1
Financing Receivable, Originated Four Years before Latest Fiscal Year	171.0	146.9
Financing Receivable, Originated Three Years before Latest Fiscal Year	80.2	163.0
Financing Receivable, Originated Two Years before Latest Fiscal Year	53.9	80.7
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	123.9	54.3
Financing Receivable, Originated in Current Fiscal Year	7.9	124.7
Financing Receivable, before Allowance for Credit Loss	1,324.8	1,348.7
Financing Receivable, Allowance for Credit Losses, Mortgage Loans	2.4	2.6	$ 3.0	$ 3.4
Loan To Value Ratio Above 65 To 75 Percent
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	1,070.6	1,076.8
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	211.4	115.7
Financing Receivable, Originated Four Years before Latest Fiscal Year	205.4	115.4
Financing Receivable, Originated Three Years before Latest Fiscal Year	278.5	215.4
Financing Receivable, Originated Two Years before Latest Fiscal Year	125.7	280.1
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	227.8	126.4
Financing Receivable, Originated in Current Fiscal Year	26.3	228.5
Financing Receivable, before Allowance for Credit Loss	1,075.1	1,081.5
Financing Receivable, Allowance for Credit Losses, Mortgage Loans	4.5	4.7	6.3	7.3
Loan To Value Ratio Above 75 To 85 Percent
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	124.1	114.9
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	124.8	89.3
Financing Receivable, Originated Four Years before Latest Fiscal Year	0.0	26.3
Financing Receivable, Originated Three Years before Latest Fiscal Year	0.0	0.0
Financing Receivable, Originated Two Years before Latest Fiscal Year	0.0	0.0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	0.0	0.0
Financing Receivable, Originated in Current Fiscal Year	0.0	0.0
Financing Receivable, before Allowance for Credit Loss	124.8	115.6
Financing Receivable, Allowance for Credit Losses, Mortgage Loans	0.7	0.7	1.2	1.3
Loan To Value Ratio Above 85 Percent
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	12.4	22.6
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	6.7	0.0
Financing Receivable, Originated Four Years before Latest Fiscal Year	6.0	16.9
Financing Receivable, Originated Three Years before Latest Fiscal Year	0.0	6.0
Financing Receivable, Originated Two Years before Latest Fiscal Year	0.0	0.0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	0.0	0.0
Financing Receivable, Originated in Current Fiscal Year	0.0	0.0
Financing Receivable, before Allowance for Credit Loss	12.7	22.9
Financing Receivable, Allowance for Credit Losses, Mortgage Loans	0.3	0.3	$ 1.0	$ 1.1
Originated Five or More Years before Last Fiscal Year
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	1,227.2	981.5
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	3.6	2.6
Originated Four Years before Last Fiscal Year
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	381.0	304.1
Originated Four Years before Last Fiscal Year \| Commercial Real Estate
Mortgage Loans on Real Estate
Financing Receivable, Allowance for Credit Losses, Mortgage Loans	1.4	1.4
Originated Three Years before Last Fiscal Year
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	357.3	383.0
Originated Three Years before Last Fiscal Year \| Commercial Real Estate
Mortgage Loans on Real Estate
Financing Receivable, Allowance for Credit Losses, Mortgage Loans	1.4	1.4
Originated Two Years before Last Fiscal Year
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	179.0	359.4
Originated Two Years before Last Fiscal Year \| Commercial Real Estate
Mortgage Loans on Real Estate
Financing Receivable, Allowance for Credit Losses, Mortgage Loans	0.6	1.4
Originated in Fiscal Year before Latest Fiscal Year
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	350.9	180.0
Originated in Fiscal Year before Latest Fiscal Year \| Commercial Real Estate
Mortgage Loans on Real Estate
Financing Receivable, Allowance for Credit Losses, Mortgage Loans	0.8	0.7
Originated in Current Fiscal Year
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	34.1	352.4
Originated in Current Fiscal Year \| Commercial Real Estate
Mortgage Loans on Real Estate
Financing Receivable, Allowance for Credit Losses, Mortgage Loans	0.1	0.8
AA Credit Rating
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	27.2	27.3
AA Credit Rating \| Commercial Real Estate
Mortgage Loans on Real Estate
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	3.3	3.3
Financing Receivable, Originated Four Years before Latest Fiscal Year	23.9	0.0
Financing Receivable, Originated Three Years before Latest Fiscal Year	0.0	24.0
Financing Receivable, Originated Two Years before Latest Fiscal Year	0.0	0.0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	0.0	0.0
Financing Receivable, Originated in Current Fiscal Year	0.0	0.0
Financing Receivable, before Allowance for Credit Loss	27.2	27.3
A Credit Rating
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	702.4	709.6
A Credit Rating \| Commercial Real Estate
Mortgage Loans on Real Estate
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	489.6	414.6
Financing Receivable, Originated Four Years before Latest Fiscal Year	78.6	68.0
Financing Receivable, Originated Three Years before Latest Fiscal Year	28.6	71.1
Financing Receivable, Originated Two Years before Latest Fiscal Year	17.5	28.9
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	81.4	17.6
Financing Receivable, Originated in Current Fiscal Year	7.9	110.6
Financing Receivable, before Allowance for Credit Loss	703.6	710.8
BBB Credit Rating
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	1,779.1	1,802.6
BBB Credit Rating \| Commercial Real Estate
Mortgage Loans on Real Estate
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	722.9	561.2
Financing Receivable, Originated Four Years before Latest Fiscal Year	273.9	227.3
Financing Receivable, Originated Three Years before Latest Fiscal Year	330.1	283.3
Financing Receivable, Originated Two Years before Latest Fiscal Year	162.1	331.9
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	270.3	163.1
Financing Receivable, Originated in Current Fiscal Year	26.3	242.6
Financing Receivable, before Allowance for Credit Loss	1,785.6	1,809.4
BB Credit Rating
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	20.8	20.9
BB Credit Rating \| Commercial Real Estate
Mortgage Loans on Real Estate
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	15.0	5.0
Financing Receivable, Originated Four Years before Latest Fiscal Year	6.0	10.2
Financing Receivable, Originated Three Years before Latest Fiscal Year	0.0	6.0
Financing Receivable, Originated Two Years before Latest Fiscal Year	0.0	0.0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	0.0	0.0
Financing Receivable, Originated in Current Fiscal Year	0.0	0.0
Financing Receivable, before Allowance for Credit Loss	$ 21.0	$ 21.2