Consolidated Supplementary Insurance Information (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	Jan. 01, 2010
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]
Decrease in deferred policy acquisition costs due to the adoption of new accounting guidance	$ 420

The decrease in deferred policy acquisition costs due to the adoption of new accounting guidance related to the accounting for costs associated with acquiring or renewing insurance contracts.

No definition available.

Name:	cb_DecreaseInDeferredPolicyAcquisitionCostsDueToAdoptionOfNewAccountingGuidance
Namespace Prefix:	cb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant