Retroactive reinsurance contracts - Narrative (Detail) - Retroactive Reinsurance [Member] - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021
Effects Of Reinsurance [Line Items]
Incurred losses and loss adjustment expenses, prior accident years	$ 208	$ 247
NICO [Member] \| AIG [Member]
Effects Of Reinsurance [Line Items]
Unpaid losses and loss adjustment expenses under retroactive reinsurance contracts	15,400		$ 15,800
Deferred charges - retroactive reinsurance	$ 4,340		$ 4,450

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.

+ Details

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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.

+ Details

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- Definition

Amount, after effects of reinsurance, of expense (reversal of expense) for claims incurred in prior reporting periods and related claims settlement costs.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 40
-Section 50
-Paragraph 3
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=116884095&loc=d3e14764-158437

+ Details

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- Details

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- Details

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- Details

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