Commitments, Contingencies, And Guarantees (Narrative) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2011	Sep. 30, 2012
Commitments Contingencies And Guarantees [Line Items]
Carrying value of limited partnerships and partially-owned investment companies included in other investments		$ 1,654
Funding commitments relating to limited partnerships and partially-owned investment companies		1,168
Case settlement	$ 1.97

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

No definition available.

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