Premiums Receivable - Premiums Receivable and Agents' Balances (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
Premiums Receivable, Gross	$ 4,550	$ 4,420	$ 4,529
Premium Receivable, Allowance for Credit Loss	(105)	(152)	(145)
Premiums Receivable, Net	4,445	4,268	4,384
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	4,130	3,851
Premium Receivable, Allowance for Credit Loss	(83)	(117)	(85)
Premiums Receivable, Loss Within a Deductible and Retrospectively-Rated Policy Premiums [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Premiums Receivable, Gross	420	569
Premium Receivable, Allowance for Credit Loss	(22)	(35)	$ (60)
Premiums Receivable, Loss Within a Deductible and Retrospectively-Rated Policy Premiums [Member] \| Standard & Poor's, AAA Rating [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Premiums Receivable, Gross	0	0
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	130	142
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	52	62
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	133	185
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	64	115
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	$ 41	$ 65

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- Definition

The carrying value as of the balance sheet date of the estimated valuation allowance to reduce gross premiums receivable to net realizable value.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(5))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 13
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=124255953&loc=SL82919249-210447

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 13
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=124255953&loc=SL82919249-210447

Reference 4: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123577603&loc=SL6953423-111524

Reference 5: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=123577603&loc=d3e5074-111524

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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.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
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Gross amount, as of the balance sheet date, due the entity from (a) agents and insureds, (b) uncollected premiums and (c) others, before deducting the allowance for doubtful accounts.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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