Fair Values of Financial Instruments - Additional Information (Detail)	Jun. 30, 2015	Dec. 31, 2014
Debt Instrument Fair Value Carrying Value [Abstract]
Percentage of fair value amounts for fixed maturities provided by a pricing service	99.00%	99.00%

The percentage of fair value amounts for fixed maturities provided by a pricing service.

No definition available.

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