Amount, after valuation allowance, recoverable under reinsurance contracts including premium paid under reinsurance contracts. Examples include, but are not limited to, settled and unsettled claims, incurred but not reported losses, loss adjustment expense, premium paid, policy benefits and policy reserves.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 944
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479838/944-20-50-5

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 944
-SubTopic 310
-Name Accounting Standards Codification
-Section 45
-Paragraph 5
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479616/944-310-45-5

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 944
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(6))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479440/944-210-S99-1

Name:	us-gaap_ReinsuranceRecoverables
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Subsequent Event (Details) - USD ($) $ in Millions	3 Months Ended
Subsequent Event (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2023	Dec. 31, 2022	Jan. 01, 2020
Subsequent Event [Abstract]
Reinsurance recoverable		$ 5,412	$ 5,416
Non-insurance warranty – CNA Financial \| Loss Portfolio Transfer for Workers' Compensation Liabilities
Subsequent Event [Abstract]
Reinsurance recoverable		$ 690		$ 690
Loss contingency, after tax and noncontrolling interests	$ 11
Non-insurance warranty – CNA Financial \| Loss Portfolio Transfer for Workers' Compensation Liabilities \| Maximum
Subsequent Event [Abstract]
Reinsurance recoverable				$ 1,000