XML 88 R74.htm IDEA: XBRL DOCUMENT
v3.25.0.1

Investments in Fixed Maturity Securities (Narrative) (Details) $ in Millions | Dec. 31, 2024 USD ($)
--- | ---
Schedule of Available-for-sale and Held-to-maturity Securities [Table] [Line Items] |
Debt Securities, Held-to-maturity, Restricted | $ 1,223
Insurance |
Schedule of Available-for-sale and Held-to-maturity Securities [Table] [Line Items] |
Debt Securities, Held-to-maturity, Restricted | 884
Reinsurance & Monoline Excess |
Schedule of Available-for-sale and Held-to-maturity Securities [Table] [Line Items] |
Debt Securities, Held-to-maturity, Restricted | 33
Letters of Credit Outstanding, Amount | 27
523991 Trust, Fiduciary, and Custody Activities |
Schedule of Available-for-sale and Held-to-maturity Securities [Table] [Line Items] |
Debt Securities, Held-to-maturity, Restricted | $ 2,167

X
- Definition Amount of restricted investment in debt security measured at amortized cost (held-to-maturity). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 860 -SubTopic 30 -Name Accounting Standards Codification -Section 50 -Paragraph 1A -Subparagraph (b)(1)(i) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481420/860-30-50-1A Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 954 -SubTopic 210 -Name Accounting Standards Codification -Section 45 -Paragraph 4 -Publisher FASB -URI https://asc.fasb.org/1943274/2147477220/954-210-45-4 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 954 -SubTopic 210 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Publisher FASB -URI https://asc.fasb.org/1943274/2147478600/954-210-50-2 + Details
Name: | us-gaap_HeldToMaturitySecuritiesRestricted
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition The total amount of the contingent obligation under letters of credit outstanding as of the reporting date. + References No definition available. + Details
Name: | us-gaap_LettersOfCreditOutstandingAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition [Line Items] for Schedule of Available-for-sale and Held-to-maturity Securities [Table] [Table] + References No definition available. + Details
Name: | wrb_ScheduleofAvailableforsaleandHeldtomaturitySecuritiesTableLineItems
Namespace Prefix: | wrb_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=wrb_InsuranceSegmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=wrb_ReinsuranceandMonolineExcessSegmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=naics_ZZ523991
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |