Invested Assets - Realized Investment Gains and Losses (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Investments, Debt and Equity Securities [Abstract]
Fixed maturities, Gross realized gains	$ 13cb_GrossRealizedGainsFixedMaturities	$ 8cb_GrossRealizedGainsFixedMaturities
Fixed maturities, Gross realized losses	(5)cb_GrossRealizedLossesFixedMaturities	(11)cb_GrossRealizedLossesFixedMaturities
Fixed maturities, Other-than-temporary impairment losses	(1)
Total fixed maturities	7	(3)
Equity securities, Gross realized gains	16cb_GrossRealizedGainsEquitySecurities	66cb_GrossRealizedGainsEquitySecurities
Equity securities, Other-than-temporary impairment losses	(22)
Total equity securities	(6)cb_GrossGainLossEquitySecurities	66cb_GrossGainLossEquitySecurities
Other invested assets	10cb_OtherInvestedAssetsGainLoss	53cb_OtherInvestedAssetsGainLoss
Total Realized Investment Gains, Net	$ 11us-gaap_GainLossOnInvestments	$ 116us-gaap_GainLossOnInvestments

The gross realized gain or loss, net, for equity securities included in earnings for the period.

No definition available.

Name:	cb_GrossGainLossEquitySecurities
Namespace Prefix:	cb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The gross realized gain or loss, net, for fixed maturities included in earnings for the period.

+ References

No definition available.

+ Details

Name:	cb_GrossGainLossOtherThanTemporaryImpairmentFixedMaturities
Namespace Prefix:	cb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

This item represents the gross profit realized on the sale of equity securities categorized neither as held-to-maturity nor trading securities.

+ References

No definition available.

+ Details

Name:	cb_GrossRealizedGainsEquitySecurities
Namespace Prefix:	cb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

This item represents the gross profit realized on the sale of fixed maturities categorized neither as held-to-maturity nor trading securities.

+ References

No definition available.

+ Details

Name:	cb_GrossRealizedGainsFixedMaturities
Namespace Prefix:	cb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

This item represents the gross loss realized on the sale of fixed maturities categorized neither as held-to-maturity nor trading securities.

+ References

No definition available.

+ Details

Name:	cb_GrossRealizedLossesFixedMaturities
Namespace Prefix:	cb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The amount charged to income if the decline in fair value for equity securities is deemed to be other than temporary.

+ References

No definition available.

+ Details

Name:	cb_ImpairmentOfInvestmentsEquitySecurities
Namespace Prefix:	cb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The amount charged to income if the decline in fair value for fixed maturities is deemed to be other than temporary.

+ References

No definition available.

+ Details

Name:	cb_ImpairmentOfInvestmentsFixedMaturities
Namespace Prefix:	cb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

This item represents the gross realized gain (loss) included in earnings for the period as a result of selling or holding other invested assets.

+ References

No definition available.

+ Details

Name:	cb_OtherInvestedAssetsGainLoss
Namespace Prefix:	cb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

This item represents the net total realized and unrealized gain (loss) included in earnings for the period as a result of selling or holding marketable securities categorized as trading, available-for-sale, or held-to-maturity, including the unrealized holding gain (loss) of held-to-maturity securities transferred to the trading security category and the cumulative unrealized gain (loss) which was included in other comprehensive income (a separate component of shareholders' equity) for available-for-sale securities transferred to trading securities during the period. Additionally, this item would include any gains (losses) realized during the period from the sale of investments accounted for under the cost method of accounting and losses recognized for other than temporary impairments (OTTI) of the subject investments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.7(c),9(a))

-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 10

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27405-111563

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 9

-Subparagraph (c)-(e)

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27357-111563

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 7

-Article 5

+ Details

Name:	us-gaap_GainLossOnInvestments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	us-gaap_InvestmentsDebtAndEquitySecuritiesAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration