Allowance for Credit Losses on Commercial Mortgage Loans (Detail) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2021	Mar. 31, 2020
Financing Receivable Allowance For Credit Losses [Line Items]
Beginning balance	$ 1.4	$ 0.0
Provision for credit losses	0.2	1.2
Charge-offs	0.0	0.0
Recoveries	0.0	0.0
Ending balance	1.6	2.0
Accounting Standards Update 2016-13 \| Cumulative Effect, Period of Adoption, Adjusted Balance
Financing Receivable Allowance For Credit Losses [Line Items]
Beginning balance	$ 0.0	$ 0.8

Amount of recovery of loans and lease receivables which had previously been fully or partially written-off as bad debts.

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-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)(4)
-URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953423-111524

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- Definition

The reserve to cover probable credit losses related to specifically identified fixed maturity real estate loans as well as probable credit losses inherent in the remainder of that loan portfolio.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 310
-Section 45
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Amount of loans and leases that have been written off from both loan receivables and allowance reserve for credit loss.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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Amount of expense related to estimated loss from loan and lease transactions.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
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