Reserve for Property and Casualty Insurance Claims and Claims Expense - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2024	Mar. 31, 2023
Catastrophe
Increase (decrease) in claims and claims expense
Losses from catastrophes, net of recoveries	$ 731	$ 1,690

Amount, after effects of reinsurance, of expense (reversal of expense) for claims incurred and costs incurred in the claim settlement process.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 944
-SubTopic 40
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480081/944-40-50-3

Name:	us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaims1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration