Invested Assets (Details) (USD $) In Millions	Jun. 30, 2011	Dec. 31, 2010
Amortized cost and fair value of fixed maturities and equity securities [Abstract]
Tax exempt, Amortized cost	$ 19,216	$ 19,072
Tax exempt, Gross unrealized appreciation	1,008	824
Tax exempt, Gross unrealized depreciation	60	122
Tax exempt, Fair value	20,164	19,774
Taxable, Amortized cost	16,440	15,989
Taxable, Gross unrealized appreciation	806	806
Taxable, Gross unrealized depreciation	43	50
Taxable, Fair value	17,203	16,745
Total fixed maturities, Amortized cost	35,656	35,061
Total fixed maturities, Gross unrealized appreciation	1,814	1,630
Total fixed maturities, Gross unrealized depreciation	103	172
Total fixed maturities, Fair value	37,367	36,519
Equity securities, Cost	1,292	1,285
Equity securities, Gross unrealized appreciation	421	340
Equity securities, Gross unrealized depreciation	50	75
Equity securities, Fair value	1,663	1,550
U.S. Government and government agency and authority obligations [Member]
Amortized cost and fair value of fixed maturities and equity securities [Abstract]
Taxable, Amortized cost	803	807
Taxable, Gross unrealized appreciation	36	31
Taxable, Gross unrealized depreciation	7	9
Taxable, Fair value	832	829
Corporate bonds [Member]
Amortized cost and fair value of fixed maturities and equity securities [Abstract]
Taxable, Amortized cost	6,453	6,258
Taxable, Gross unrealized appreciation	419	411
Taxable, Gross unrealized depreciation	17	21
Taxable, Fair value	6,855	6,648
Foreign government and government agency obligations [Member]
Amortized cost and fair value of fixed maturities and equity securities [Abstract]
Taxable, Amortized cost	6,312	5,943
Taxable, Gross unrealized appreciation	222	231
Taxable, Gross unrealized depreciation	12	13
Taxable, Fair value	6,522	6,161
Residential Mortgage-Backed Securities [Member]
Amortized cost and fair value of fixed maturities and equity securities [Abstract]
Taxable, Amortized cost	1,061	1,293
Taxable, Gross unrealized appreciation	53	63
Taxable, Gross unrealized depreciation	6	6
Taxable, Fair value	1,108	1,350
Commercial Mortgage-Backed Securities [Member]
Amortized cost and fair value of fixed maturities and equity securities [Abstract]
Taxable, Amortized cost	1,811	1,688
Taxable, Gross unrealized appreciation	76	70
Taxable, Gross unrealized depreciation	1	1
Taxable, Fair value	$ 1,886	$ 1,757

Name:	cb_AmortizedCostAndFairValueOfInvestedAssetsAbstract
Namespace Prefix:	cb
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

This item represents the cost basis of equity securities.

+ Details

Name:	cb_EquitySecuritiesCost
Namespace Prefix:	cb
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The excess of the fair value of equity securities over its amortized cost which excess value has not been recognized in earnings of the entity.

+ Details

Name:	cb_EquitySecuritiesGrossUnrealizedAppreciation
Namespace Prefix:	cb
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The excess of amortized cost of equity securities over its fair value which deficiency has not been recognized in earnings of the entity.

+ Details

Name:	cb_EquitySecuritiesGrossUnrealizedDepreciation
Namespace Prefix:	cb
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

This item represents total fixed maturities that are categorized as neither held-to-maturity nor trading. Such securities are reported at fair value; unrealized gains and losses of such securities are excluded from earnings and included in other comprehensive income.

+ Details

Name:	cb_FixedMaturities
Namespace Prefix:	cb
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

This item represents the amortized cost basis of investments in debt securities having predetermined or determinable maturity dates.

+ Details

Name:	cb_FixedMaturitiesCost
Namespace Prefix:	cb
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The excess of the fair value of fixed maturities over its amortized cost which excess value has not been recognized in earnings of the entity.

+ Details

Name:	cb_FixedMaturitiesGrossUnrealizedAppreciation
Namespace Prefix:	cb
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The excess of amortized cost of fixed maturities over its fair value which deficiency has not been recognized in earnings of the entity.

+ Details

Name:	cb_FixedMaturitiesGrossUnrealizedDepreciation
Namespace Prefix:	cb
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

This item represents total taxable debt securities that are categorized as neither held-to-maturity nor trading. Such securities are reported at fair value; unrealized gains and losses of such securities are excluded from earnings and included in other comprehensive income.

+ Details

Name:	cb_Taxable
Namespace Prefix:	cb
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

This item represents the amortized cost basis of taxable debt securities that are categorized as neither held-to-maturity nor trading.

+ Details

Name:	cb_TaxableCost
Namespace Prefix:	cb
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The excess of the fair value of taxable fixed maturities over its amortized cost which excess value has not been recognized in earnings of the entity.

+ Details

Name:	cb_TaxableGrossUnrealizedAppreciation
Namespace Prefix:	cb
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The excess of amortized cost of taxable fixed maturities over its fair value which deficiency has not been recognized in earnings of the entity.

+ Details

Name:	cb_TaxableGrossUnrealizedDepreciation
Namespace Prefix:	cb
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

This item represents total tax-exempt debt securities that are categorized as neither held-to-maturity nor trading. Such securities are reported at fair value; unrealized gains and losses of such securities are excluded from earnings and included in other comprehensive income.

+ Details

Name:	cb_TaxExempt
Namespace Prefix:	cb
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

This item represents the amortized cost basis of tax exempt debt securities that are categorized as neither held-to-maturity nor trading.

+ Details

Name:	cb_TaxExemptCost
Namespace Prefix:	cb
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The excess of the fair value of tax exempt fixed maturities over its amortized cost which excess value has not been recognized in earnings of the entity.

+ Details

Name:	cb_TaxExemptGrossUnrealizedAppreciation
Namespace Prefix:	cb
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The excess of amortized cost of tax exempt fixed maturities over its fair value which deficiency has not been recognized in earnings of the entity.

+ Details

Name:	cb_TaxExemptGrossUnrealizedDepreciation
Namespace Prefix:	cb
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

For an unclassified balance sheet, this item represents equity securities categorized neither as held-to-maturity nor trading. Equity securities represent ownership interests or the right to acquire ownership interests in corporations and other legal entities which ownership interest is represented by shares of common or preferred stock (which is not mandatorily redeemable or redeemable at the option of the holder), convertible securities, stock rights, or stock warrants. Unrealized gains and losses related to Available-for-sale Securities are excluded from earnings and reported in a separate component of shareholders' equity (other comprehensive income), unless the Available-for-sale Security is designated as a hedge or is determined to have had an other than temporary decline in fair value below its amortized cost basis. All or a portion of the unrealized holding gain or loss of an Available-for-sale Security that is designated as being hedged in a fair value hedge shall be recognized in earnings during the period of the hedge, as should other than temporary declines in fair value below costs basis.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 133
-Paragraph 22

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 115
-Paragraph 19

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 115
-Paragraph 12
-Subparagraph b

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Emerging Issues Task Force (EITF)
-Number 86-40

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 115
-Paragraph 13

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 115
-Paragraph 16

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 115
-Paragraph 3
-Subparagraph c

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesEquitySecurities
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant