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Condensed Financial Information of Parent Company - Statements of Cash Flows (Parenthetical) (Detail) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2013
Condensed Financial Statements, Captions [Line Items]  
Cash $ 52us-gaap_Cash
Alterra Common Stock [Member]  
Condensed Financial Statements, Captions [Line Items]  
Holdings of common stock and warrants, cost basis 177us-gaap_TransferOfInvestments
/ us-gaap_ConversionOfStockByUniqueDescriptionAxis
= cb_AlterraCapitalHoldingsLimitedMember
Alterra Warrants [Member]  
Condensed Financial Statements, Captions [Line Items]  
Holdings of common stock and warrants, cost basis 63us-gaap_TransferOfInvestments
/ us-gaap_ConversionOfStockByUniqueDescriptionAxis
= cb_AlterraWarrantsMember
Markel Corporation [Member]  
Condensed Financial Statements, Captions [Line Items]  
Transferred, common stock value 226us-gaap_TransferToInvestments
/ us-gaap_ConversionOfStockByUniqueDescriptionAxis
= cb_MarkelCorporationMember
Cash $ 98us-gaap_Cash
/ us-gaap_ConversionOfStockByUniqueDescriptionAxis
= cb_MarkelCorporationMember