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.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 326
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The carrying value as of the balance sheet date of the estimated valuation allowance to reduce gross premiums receivable to net realizable value.

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Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 944
-SubTopic 210
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The carrying amount as of the balance sheet date due the entity from (a) agents and insureds, (b) uncollected premiums and (c) others, net of the allowance for doubtful accounts.

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Premiums Receivable - Premiums Receivable and Agents' Balances (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Financing Receivable, Credit Quality Indicator [Line Items]
Premiums Receivable, Gross	$ 5,716	$ 5,058
Premium Receivable, Allowance for Credit Loss	(109)	(109)	$ (105)	$ (152)
Premiums Receivable, Net	5,607	4,949
Premiums Receivable, Due in One Year or Less, Excluding Receivables for Loss within a Deductible and Retrospectively-Rated Policy Premiums [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Premiums Receivable, Gross	5,303	4,698
Premium Receivable, Allowance for Credit Loss	(89)	(85)	(83)	(117)
Premiums Receivable, Loss Within a Deductible and Retrospectively-Rated Policy Premiums [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Premiums Receivable, Gross	413	360
Premium Receivable, Allowance for Credit Loss	(20)	(24)	$ (22)	$ (35)
Premiums Receivable, Loss Within a Deductible and Retrospectively-Rated Policy Premiums [Member] \| Standard & Poor's, AA Rating
Financing Receivable, Credit Quality Indicator [Line Items]
Premiums Receivable, Gross	94	106
Premiums Receivable, Loss Within a Deductible and Retrospectively-Rated Policy Premiums [Member] \| Standard & Poor's, A Rating [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Premiums Receivable, Gross	54	38
Premiums Receivable, Loss Within a Deductible and Retrospectively-Rated Policy Premiums [Member] \| Standard & Poor's, BBB Rating
Financing Receivable, Credit Quality Indicator [Line Items]
Premiums Receivable, Gross	136	119
Premiums Receivable, Loss Within a Deductible and Retrospectively-Rated Policy Premiums [Member] \| Standard & Poor's, BB Rating
Financing Receivable, Credit Quality Indicator [Line Items]
Premiums Receivable, Gross	84	56
Premiums Receivable, Loss Within a Deductible and Retrospectively-Rated Policy Premiums [Member] \| Standard & Poor's, Below BB Rating
Financing Receivable, Credit Quality Indicator [Line Items]
Premiums Receivable, Gross	$ 45	$ 41