Fair Values of Financial Instruments - Additional Information (Detail)	Sep. 30, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Percentage of fair value amounts for fixed maturities provided by a pricing service	99.00%

Percentage of fair value amounts for fixed maturities provided by pricing service.

No definition available.

Name:	cb_PercentageOfFairValueAmountsForFixedMaturitiesProvidedByPricingService
Namespace Prefix:	cb_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant