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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	Sep. 30, 2021	Jun. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Jan. 01, 2020
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	$ 2,499.4		$ 2,432.1
Loan to Value Ratio Below or Equal to 65 Percent
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	1,256.7		1,189.4
Loan To Value Ratio Above 65 To 75 Percent
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	1,048.2		1,000.3
Loan To Value Ratio Above 75 To 85 Percent
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	156.4		155.8
Loan To Value Ratio Above 85 Percent
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	38.1		86.6
Originated Five or More Years before Last Fiscal Year
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	1,043.6
Originated Four Years before Last Fiscal Year
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	305.7
Originated Three Years before Last Fiscal Year
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	384.3
Originated Two Years before Last Fiscal Year
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	360.8
Originated in Fiscal Year before Latest Fiscal Year
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	180.7
Originated in Current Fiscal Year
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	224.3
Commercial Real Estate
Mortgage Loans on Real Estate
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	1,047.2
Financing Receivable, Originated Four Years before Latest Fiscal Year	307.6
Financing Receivable, Originated Three Years before Latest Fiscal Year	386.4
Financing Receivable, Originated Two Years before Latest Fiscal Year	362.8
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	181.7
Financing Receivable, Originated in Current Fiscal Year	225.0
Financing Receivable, before Allowance for Credit Loss	2,510.7		2,445.2
Financing Receivable, Allowance for Credit Losses, Mortgage Loans	11.3
Commercial Real Estate \| Loan to Value Ratio Below or Equal to 65 Percent
Mortgage Loans on Real Estate
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	810.6
Financing Receivable, Originated Four Years before Latest Fiscal Year	139.4
Financing Receivable, Originated Three Years before Latest Fiscal Year	110.3
Financing Receivable, Originated Two Years before Latest Fiscal Year	81.2
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	54.6
Financing Receivable, Originated in Current Fiscal Year	63.8
Financing Receivable, before Allowance for Credit Loss	1,259.9
Financing Receivable, Allowance for Credit Losses, Mortgage Loans	3.2	$ 3.2	3.4	$ 3.9	$ 3.9	$ 2.8
Commercial Real Estate \| Loan To Value Ratio Above 65 To 75 Percent
Mortgage Loans on Real Estate
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	110.8
Financing Receivable, Originated Four Years before Latest Fiscal Year	103.7
Financing Receivable, Originated Three Years before Latest Fiscal Year	270.0
Financing Receivable, Originated Two Years before Latest Fiscal Year	281.6
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	127.1
Financing Receivable, Originated in Current Fiscal Year	161.2
Financing Receivable, before Allowance for Credit Loss	1,054.4
Financing Receivable, Allowance for Credit Losses, Mortgage Loans	6.2	6.2	7.3	9.1	7.9	4.6
Commercial Real Estate \| Loan To Value Ratio Above 75 To 85 Percent
Mortgage Loans on Real Estate
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	110.3
Financing Receivable, Originated Four Years before Latest Fiscal Year	47.5
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	157.8
Financing Receivable, Allowance for Credit Losses, Mortgage Loans	1.4	1.5	1.3	0.7	1.0	0.5
Commercial Real Estate \| Loan To Value Ratio Above 85 Percent
Mortgage Loans on Real Estate
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	15.5
Financing Receivable, Originated Four Years before Latest Fiscal Year	17.0
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	38.6
Financing Receivable, Allowance for Credit Losses, Mortgage Loans	0.5	$ 0.5	1.1	$ 0.9	$ 0.4	$ 0.4
Commercial Real Estate \| Originated Five or More Years before Last Fiscal Year
Mortgage Loans on Real Estate
Financing Receivable, Allowance for Credit Losses, Mortgage Loans	3.6
Commercial Real Estate \| Originated Four Years before Last Fiscal Year
Mortgage Loans on Real Estate
Financing Receivable, Allowance for Credit Losses, Mortgage Loans	1.9
Commercial Real Estate \| Originated Three Years before Last Fiscal Year
Mortgage Loans on Real Estate
Financing Receivable, Allowance for Credit Losses, Mortgage Loans	2.1
Commercial Real Estate \| Originated Two Years before Last Fiscal Year
Mortgage Loans on Real Estate
Financing Receivable, Allowance for Credit Losses, Mortgage Loans	2.0
Commercial Real Estate \| Originated in Fiscal Year before Latest Fiscal Year
Mortgage Loans on Real Estate
Financing Receivable, Allowance for Credit Losses, Mortgage Loans	1.0
Commercial Real Estate \| Originated in Current Fiscal Year
Mortgage Loans on Real Estate
Financing Receivable, Allowance for Credit Losses, Mortgage Loans	0.7
AA Credit Rating
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	3.3		3.5
AA Credit Rating \| Commercial Real Estate
Mortgage Loans on Real Estate
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	3.3
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	3.3
A Credit Rating
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	487.3		510.0
A Credit Rating \| Commercial Real Estate
Mortgage Loans on Real Estate
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	331.1
Financing Receivable, Originated Four Years before Latest Fiscal Year	59.8
Financing Receivable, Originated Three Years before Latest Fiscal Year	63.6
Financing Receivable, Originated Two Years before Latest Fiscal Year	16.1
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	17.7
Financing Receivable, Originated in Current Fiscal Year	0.0
Financing Receivable, before Allowance for Credit Loss	488.3
BBB Credit Rating
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	1,967.0		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	681.0
Financing Receivable, Originated Four Years before Latest Fiscal Year	237.6
Financing Receivable, Originated Three Years before Latest Fiscal Year	322.8
Financing Receivable, Originated Two Years before Latest Fiscal Year	346.7
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	164.0
Financing Receivable, Originated in Current Fiscal Year	225.0
Financing Receivable, before Allowance for Credit Loss	1,977.1
BB Credit Rating
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	26.3		39.4
BB Credit Rating \| Commercial Real Estate
Mortgage Loans on Real Estate
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	16.3
Financing Receivable, Originated Four Years before Latest Fiscal Year	10.2
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	26.5
B Credit Rating
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	15.5		$ 16.2
B Credit Rating \| Commercial Real Estate
Mortgage Loans on Real Estate
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	15.5
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	$ 15.5