Allowance for Credit Losses and Recorded Investment in Commercial Mortgage Loans (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	$ 9
Provision		$ 0
Ending balance	13	9
Ending balance	6,933	6,700
Allowance for Credit Losses
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	9	9	$ 12
Charge-offs	0	0	0
Recoveries	0	0	0
Provision	4		(3)
Ending balance	13	9	9
Ending allowance for individually impaired loans	0	0	0
Ending allowance for loans not individually impaired that were evaluated collectively for impairment	13	9	9
Commercial Mortgage Loans Recorded Investment
Financing Receivable, Allowance for Credit Losses [Line Items]
Ending balance	6,933	6,700	6,353
Ending balance of individually impaired loans	0	3	6
Ending balance of loans not individually impaired that were evaluated collectively for impairment	$ 6,933	$ 6,697	$ 6,347

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

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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
-Topic 944
-SubTopic 310
-Section 45
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=118959141&loc=d3e21338-158488

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- Definition

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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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
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-Section S99
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-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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- Definition

The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.

+ References

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- Definition

Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.

+ References

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- Definition

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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- Definition

The balance of financing receivables that were collectively evaluated for impairment.

+ References

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- Definition

The balance of financing receivables that were individually evaluated for impairment.

+ References

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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
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- Definition

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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