v2.4.0.8

Fair Value Measurements (Financial Instruments Measured At Fair Value Using Significant Unobservable Inputs) (Detail) (USD $) In Millions, unless otherwise specified | 3 Months Ended | 9 Months Ended |  |  |  |
--- | --- | --- | --- | --- | --- | ---
Sep. 30, 2014 | Sep. 30, 2013 | Sep. 30, 2014 | Sep. 30, 2013 | Jun. 30, 2014 | Dec. 31, 2013 | Jun. 30, 2013 | Dec. 31, 2012
Equity Securities [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule Of Fair Value Measurements [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3 | $ 0 |  | $ 0 |  | $ 0 |  | $ 7 |  |  |  |  |  |  |  |  |
Balance- Beginning of Period, Assets | 2 |  | 4 |  | 4 |  | 3 |  |  |  |  |  |  |  |  |
Transfers out of Level 3, Assets | 0 |  | 0 |  | (2) |  | (1) |  |  |  |  |  |  |  |  |
Change in Net Unrealized Gains (Losses) included in OCI, Assets | 0 |  | 0 |  | 1 |  | (5) |  |  |  |  |  |  |  |  |
Net Realized Gains/Losses, Assets |  |  | 0 |  |  |  | 4 |  |  |  |  |  |  |  |  |
Purchases, Assets | 0 |  | 0 |  | 1 |  | 1 |  |  |  |  |  |  |  |  |
Sales, Assets | 0 |  | 0 |  | (2) |  | (5) |  |  |  |  |  |  |  |  |
Settlements, Assets |  |  | 0 |  |  |  |  |  |  |  |  |  |  |  |  |
Balance-End of Period, Assets | 2 |  | 4 |  | 2 |  | 4 |  |  |  |  |  |  |  |  |
Net Realized Gains/Losses Attributable to Changes in Fair Value at the Balance Sheet Date, Assets |  |  | 0 |  |  |  |  |  |  |  |  |  |  |  |  |
Short-term Investments [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule Of Fair Value Measurements [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3 |  |  | 1 |  | 0 |  | 8 |  |  |  |  |  |  |  |  |
Balance- Beginning of Period, Assets |  |  | 9 |  | 7 |  | 0 |  |  |  |  |  |  |  |  |
Transfers out of Level 3, Assets |  |  | (2) |  | (7) |  | (2) |  |  |  |  |  |  |  |  |
Purchases, Assets |  |  | 0 |  | 0 |  | 2 |  |  |  |  |  |  |  |  |
Balance-End of Period, Assets | 0 |  | 8 |  | 0 |  | 8 |  |  |  |  |  |  |  |  |
Other Long-term Investments [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule Of Fair Value Measurements [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3 | 0 |  | 0 |  | 0 |  | 0 |  |  |  |  |  |  |  |  |
Balance- Beginning of Period, Assets | 2,640 |  | 2,349 |  | 2,440 |  | 2,252 |  |  |  |  |  |  |  |  |
Transfers out of Level 3, Assets |  |  | 0 |  |  |  |  |  |  |  |  |  |  |  |  |
Change in Net Unrealized Gains (Losses) included in OCI, Assets | (8) |  | (1) |  | 40 |  | 34 |  |  |  |  |  |  |  |  |
Net Realized Gains/Losses, Assets | 0 |  | 0 |  | (3) |  | (2) |  |  |  |  |  |  |  |  |
Purchases, Assets | 170 |  | 138 |  | 522 |  | 387 |  |  |  |  |  |  |  |  |
Sales, Assets | (3) |  | (1) |  | (6) |  | (10) |  |  |  |  |  |  |  |  |
Settlements, Assets | (128) |  | (96) |  | (322) |  | (272) |  |  |  |  |  |  |  |  |
Balance-End of Period, Assets | 2,671 |  | 2,389 |  | 2,671 |  | 2,389 |  |  |  |  |  |  |  |  |
Net Realized Gains/Losses Attributable to Changes in Fair Value at the Balance Sheet Date, Assets | 0 |  | 0 |  | (3) |  | (2) |  |  |  |  |  |  |  |  |
Available-for-sale Securities [Member] | Foreign [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule Of Fair Value Measurements [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3 | 1 |  | 1 |  | 3 |  | 33 |  |  |  |  |  |  |  |  |
Balance- Beginning of Period, Assets | 12 |  | 48 |  | 44 |  | 60 |  |  |  |  |  |  |  |  |
Transfers out of Level 3, Assets | 0 |  | (8) |  | (34) |  | (49) |  |  |  |  |  |  |  |  |
Change in Net Unrealized Gains (Losses) included in OCI, Assets | 0 |  | 2 |  | (1) |  | (2) |  |  |  |  |  |  |  |  |
Net Realized Gains/Losses, Assets | 0 |  | 0 |  | 1 |  | 1 |  |  |  |  |  |  |  |  |
Purchases, Assets | 0 |  | 12 |  | 2 |  | 15 |  |  |  |  |  |  |  |  |
Sales, Assets | (1) |  | (13) |  | (3) |  | (15) |  |  |  |  |  |  |  |  |
Settlements, Assets | 0 |  | 0 |  | 0 |  | (1) |  |  |  |  |  |  |  |  |
Balance-End of Period, Assets | 12 |  | 42 |  | 12 |  | 42 |  |  |  |  |  |  |  |  |
Available-for-sale Securities [Member] | Corporate Debt Securities [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule Of Fair Value Measurements [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3 | 5 |  | 12 |  | 35 |  | 29 |  |  |  |  |  |  |  |  |
Balance- Beginning of Period, Assets | 204 |  | 114 |  | 166 |  | 102 |  |  |  |  |  |  |  |  |
Transfers out of Level 3, Assets | 0 |  | (1) |  | (22) |  | (30) |  |  |  |  |  |  |  |  |
Change in Net Unrealized Gains (Losses) included in OCI, Assets | (1) |  | (1) |  | 1 |  | (1) |  |  |  |  |  |  |  |  |
Net Realized Gains/Losses, Assets | 2 |  | (1) |  | 2 |  | (2) |  |  |  |  |  |  |  |  |
Purchases, Assets | 20 |  | 6 |  | 65 |  | 39 |  |  |  |  |  |  |  |  |
Sales, Assets | (9) |  | (4) |  | (17) |  | (4) |  |  |  |  |  |  |  |  |
Settlements, Assets | (13) |  | (4) |  | (22) |  | (12) |  |  |  |  |  |  |  |  |
Balance-End of Period, Assets | 208 |  | 121 |  | 208 |  | 121 |  |  |  |  |  |  |  |  |
Available-for-sale Securities [Member] | Mortgage Backed-Securities [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule Of Fair Value Measurements [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3 | 0 |  | 0 |  | 0 |  | 0 |  |  |  |  |  |  |  |  |
Balance- Beginning of Period, Assets | 7 |  | 9 |  | 8 |  | 13 |  |  |  |  |  |  |  |  |
Transfers out of Level 3, Assets | 0 |  | 0 |  | 0 |  | 0 |  |  |  |  |  |  |  |  |
Change in Net Unrealized Gains (Losses) included in OCI, Assets |  |  | 0 |  |  |  |  |  |  |  |  |  |  |  |  |
Net Realized Gains/Losses, Assets |  |  | 0 |  |  |  |  |  |  |  |  |  |  |  |  |
Purchases, Assets | 8 |  | 0 |  | 8 |  | 0 |  |  |  |  |  |  |  |  |
Sales, Assets | 0 |  | 0 |  | 0 |  | (3) |  |  |  |  |  |  |  |  |
Settlements, Assets | 0 |  | 0 |  | (1) |  | (1) |  |  |  |  |  |  |  |  |
Balance-End of Period, Assets | 15 |  | 9 |  | 15 |  | 9 |  |  |  |  |  |  |  |  |
Guaranteed Minimum Income Benefit [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule Of Fair Value Measurements [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value | 317 | [1] | 514 | [1] | 317 | [1] | 514 | [1] | 241 | [1] | 193 | [1] | 652 | [1] | 1,119 | [1]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings | 76 | [1] | (138) | [1] | 124 | [1] | (605) | [1] |  |  |  |  |  |  |  |
Net Realized Gains/Losses Attributable to Changes in Fair Value at the Balance Sheet Date, Liabilities | 76 |  | (138) |  | 124 |  | (605) |  |  |  |  |  |  |  |  |
Reported liabilities | $ 566 |  | $ 746 |  | $ 566 |  | $ 746 |  |  |  | $ 427 |  | $ 880 |  | $ 1,400 |
[1] | Our GLB reinsurance product meets the definition of a derivative instrument for accounting purposes and is accordingly carried at fair value. Excluded from the table above is the portion of the GLB derivative liability classified as Future policy benefits in the consolidated balance sheets. Refer to Note 5 for additional information.

X
- Definition For financial instruments held at the balance sheet date, this represents the net realized gains/losses attributable to changes in fair value of financial instruments reflected in assets and carried or disclosed at fair value using significant unobservable inputs. + References No definition available. + Details
Name: | ace_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetNetRealizedGainLossAttributableToChangesInFairValue
Namespace Prefix: | ace_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition For financial instruments held at the balance sheet date, this represents the net realized gains/losses attributable to changes in fair value of finacial instruments reflected in liabilities and carried or disclosed at fair value using significant unobservable inputs. + References No definition available. + Details
Name: | ace_FairValueMeasurementWithUnobservableInputsRreconciliationRecurringBasisLiabilityNetRealizedGainLossAttributableToChangesInFairValue
Namespace Prefix: | ace_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Details
Name: | ace_ScheduleOfFairValueMeasurementsLineItems
Namespace Prefix: | ace_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of gain (loss) recognized in the income statement for financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258 + Details
Name: | us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of gain (loss) recognized in other comprehensive income (loss) for financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1a) -URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258 + Details
Name: | us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of purchases of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258 + Details
Name: | us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount of sale of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258 + Details
Name: | us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of settlement of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258 + Details
Name: | us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of transfer of financial instrument classified as an asset into level 3 of the fair value hierarchy. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(3) -URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258 + Details
Name: | us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount of transfers of financial instrument classified as an asset out of level 3 of the fair value hierarchy. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(3) -URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258 + Details
Name: | us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Fair value of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258 + Details
Name: | us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of gain (loss) recognized on the income statement for financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258 + Details
Name: | us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Fair value of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258 + Details
Name: | us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Sum of the amount of expected guaranteed benefits in excess of the projected account balances for minimum guaranteed benefit contracts, as of the balance sheet date, net of reinsurance recoverables, for all guaranteed benefit types. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 80 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6484115&loc=d3e19393-158473 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 20 -Section 55 -Paragraph 15 -URI http://asc.fasb.org/extlink&oid=6588021&loc=d3e7104-158389 + Details
Name: | us-gaap_GuaranteedBenefitLiabilityNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant