Invested Assets - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013 Investment	Dec. 31, 2012
Investments Debt And Equity Securities [Abstract]
Approximate number of individual fixed maturities in unrealized loss position	360
Approximate number of individual equity securities in unrealized loss position	20
Cumulative credit-related losses recognized in net income	$ 22	$ 22

Cumulative credit-related losses, recognized in net income, related to fixed maturities held, for which a portion of their other-than-temporary impairment losses were recognized in other comprehensive income.

No definition available.

Name:	cb_CumulativeCreditLossesRecognizedInNetIncome
Namespace Prefix:	cb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant