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

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No definition available.

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

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No definition available.

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

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No definition available.

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Fair value, after effects of master netting arrangements, of financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset offset against the right to receive collateral. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

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Amount of rent expense incurred for leased assets, including but not limited to, furniture and equipment, that is not directly or indirectly associated with the manufacture, sale or creation of a product or product line.

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No definition available.

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The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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The maximum amount of borrowing capacity under a line of credit that is available as of the balance sheet date for a specific purpose other than for financing goods acquired for inventory or imminent delivery to a customer.

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No definition available.

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Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility.

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Amount of increase (decrease) of the credit facility.

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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.

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

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The fair value of collateral received by the entity associated with securities borrowed that must be returned if the counterparty fulfills its obligations. It appears on the balance sheet as a liability and has a corresponding asset that appears on the balance sheet called Securities Received as Collateral.

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The carrying amount (fair value) as of the balance sheet date of securities held that had been pledged by counterparties under financing and lending arrangements, pursuant to which the entity has the right by agreement or custom to sell or re-pledge such securities.

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Amount, after the effects of master netting arrangements, of funds outstanding borrowed in the form of a security repurchase agreement between the entity and another party for the sale and repurchase of identical or substantially the same securities at a date certain for a specified price. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

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Number of shares that have been repurchased during the period and are being held in treasury.

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Equity impact of the cost of common and preferred stock that were repurchased during the period. Recorded using the cost method.

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Commitments, contingencies, and guarantees (Narrative) (Detail) (USD $)	3 Months Ended	12 Months Ended
	Jun. 30, 2014	Dec. 31, 2014 derivative	Dec. 31, 2013	Dec. 31, 2012
Commitments Contingencies And Guarantees [Line Items]
Derivative Liability, Fair Value, Amount Offset Against Collateral		$ (34,000,000)	$ (41,000,000)
Securities Sold under Agreements to Repurchase		1,402,000,000	1,401,000,000
Obligation to Return Securities Received as Collateral		1,331,000,000	1,633,000,000
Securities Held as Collateral, at Fair Value		1,330,000,000	1,632,000,000
Number of in-force interest rate swaps		0
Approximate percentage of gross premiums written that were generated from or placed by Marsh		10.00%ace_ConcentrationRiskPercentageMarsh	11.00%ace_ConcentrationRiskPercentageMarsh	11.00%ace_ConcentrationRiskPercentageMarsh
Carrying value of limited partnerships and partially-owned investment companies included in other investments		2,200,000,000
Funding commitments relating to limited partnerships and partially-owned investment companies		1,000,000,000
Amount of credit facility not renewed by the company	500,000,000	425,000,000
Total rental expense related to operating leases		127,000,000us-gaap_LeaseAndRentalExpense	128,000,000us-gaap_LeaseAndRentalExpense	112,000,000us-gaap_LeaseAndRentalExpense
Letter of Credit [Member]
Commitments Contingencies And Guarantees [Line Items]
Line of Credit Facility, Current Borrowing Capacity		1,000,000,000
Letter Of Credit Unsecured Expiring November 2017 \| Letter of Credit [Member]
Commitments Contingencies And Guarantees [Line Items]
Borrowing capacity on unsecured revolving line of credit		1,500,000,000
Line of Credit Facility, Capacity Available for Specific Purpose Other than for Trade Purchases		300,000,000
Line of Credit Facility, Amount Outstanding		479,000,000
November 2013 Stock Repurchase Plan [Member]
Commitments Contingencies And Guarantees [Line Items]
Repurchase of outstanding common shares, shares		13,982,358	3,266,531	100,000
Cost of shares acquired		$ 1,449,000,000	$ 290,000,000	$ 7,000,000