Retroactive reinsurance contracts - Narrative (Detail) - Retroactive Reinsurance [Member] - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Effects of Reinsurance [Line Items]
Unamortized deferred charges of retroactive reinsurance contracts	$ 9,900	$ 10,600
Retroactive reinsurance contracts, claims paid	2,358	1,889	$ 1,076
Liabilities for environmental, asbestos and latent injury claims	12,100	12,300
AIG [Member] \| NICO [Member]
Effects of Reinsurance [Line Items]
Unpaid losses and loss adjustment expenses under retroactive reinsurance contracts	13,900	15,800
Retroactive reinsurance contracts, claims paid	$ 1,500	$ 1,200

Unpaid losses and loss adjustment expenses for retroactive reinsurance contracts.

No definition available.

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- Definition

The remaining unamortized excess of the estimated ultimate liability for claims and claim costs over the premiums earned with respect to retroactive property/casualty reinsurance contracts.

+ References

No definition available.

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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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- Definition

Carrying amount as of the balance sheet date of reserves for the costs of settling insured claims and costs incurred in the claims settlement process attributable to asbestos and environmental claims, net of estimated reinsurance recoveries.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 40
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=116884095&loc=d3e14764-158437

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-Section 50
-Paragraph 3
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-URI https://asc.fasb.org/extlink&oid=116884095&loc=d3e14764-158437

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- Definition

Amount, after effects of reinsurance, of payments to settle insured claims and pay costs incurred in the claims settlement process.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 40
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI https://asc.fasb.org/extlink&oid=116884095&loc=d3e14764-158437

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 25
-Subparagraph (g)
-URI https://asc.fasb.org/extlink&oid=126954810&loc=d3e3536-108585

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