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Data Type:	xbrli:stringItemType
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The percentage of gross premiums written that were generated from or placed by AON Corporation and its affiliates.

+ References

No definition available.

+ Details

Name:	ace_ConcentrationRiskPercentageAon
Namespace Prefix:	ace_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The percentage of gross premiums written that were generated from or placed by March, Inc. and its affiliates.

+ References

No definition available.

+ Details

Name:	ace_ConcentrationRiskPercentageMarsh
Namespace Prefix:	ace_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Fair value of the amount outstanding under the letter of credit facility.

+ References

No definition available.

+ Details

Name:	ace_LetterOfCreditFacilityFairValueOfAmountOutstanding
Namespace Prefix:	ace_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Maximum borrowing capacity under the letter of credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

No definition available.

+ Details

Name:	ace_LetterOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix:	ace_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The value of the outstanding letters of credit issued under this facility.

+ References

No definition available.

+ Details

Name:	ace_LineOfCreditFacilityLettersOfCreditIssued
Namespace Prefix:	ace_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Carrying value of limited partnerships and partially-owned investment companies included in other investments.

+ References

No definition available.

+ Details

Name:	ace_OtherInvestmentsLimitedPartnershipsAndPartiallyOwnedInvestmentCompaniesCarryingValue
Namespace Prefix:	ace_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Funding commitments relating to limited partnerships and partially-owned investment companies included in other investments.

+ References

No definition available.

+ Details

Name:	ace_OtherInvestmentsLimitedPartnershipsAndPartiallyOwnedInvestmentCompaniesFundingCommitments
Namespace Prefix:	ace_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Rental expense incurred for leased assets including furniture and equipment which has not been recognized in costs and expenses applicable to sales and revenues; for example, cost of goods sold or other operating costs and expenses.

+ References

No definition available.

+ Details

Name:	us-gaap_LeaseAndRentalExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 129

-Paragraph 2, 4

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 22

-Article 5

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.19(b),22(b))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

This element represents the expenses incurred by the entity which are directly related and attributable to receiving an award in settlement of litigation.

+ References

No definition available.

+ Details

Name:	us-gaap_LitigationSettlementExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Number of interest rate derivative instruments held by the entity at the reporting date.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 1B

-URI http://asc.fasb.org/extlink&oid=6935481&loc=SL5580258-113959

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 1A

-Subparagraph (d)

-URI http://asc.fasb.org/extlink&oid=6935481&loc=SL5579245-113959

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Commitments, Contingencies, And Guarantees (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Commitments Contingencies And Guarantees [Line Items]
Interest rate swaps in force	0
Concentration risk - Marsh Inc	12.00%
Concentration risk - AON Corporation	10.00%
Carrying value of limited partnerships and partially-owned investment companies included in other investments	$ 1,435
Funding commitments relating to limited partnerships and partially-owned investment companies	777
Revolving credit facilities, maximum	500
Revolving credit facility - LOC	55
Operating leases, rent expense	114	83	84
Case settlement	1.97
Letter Of Credit Unsecured Expiring November 2012 [Member]
Commitments Contingencies And Guarantees [Line Items]
Letter of credit - maximum	1,000
Letter of credit - utilized	948
Letter Of Credit Unsecured Expiring September 2014 [Member]
Commitments Contingencies And Guarantees [Line Items]
Letter of credit - maximum	500
Letter Of Credit Bilateral Uncollateralized Expiring December 2015 [Member]
Commitments Contingencies And Guarantees [Line Items]
Letter of credit - maximum	400
Letter of credit - utilized	$ 392