Reinsurance (Reinsurance Recoverable on Ceded Reinsurance) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Reinsurance Disclosures [Abstract]
Reinsurance recoverable on unpaid losses and loss expenses	$ 11,399	$ 11,602	$ 12,149	$ 12,745
Reinsurance recoverable on paid losses and loss expenses	679	787
Net reinsurance recoverable on losses and loss expenses	$ 12,078	$ 12,389

The known and estimated amount recoverable as of the balance sheet date from reinsurers for claims paid or incurred by the ceding insurer and associated claims settlement expenses, including estimated amounts for claims incurred but not reported net of any related valuation allowance.

No definition available.

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