Significant Accounting Policies (Details)	3 Months Ended
Mar. 31, 2014
Significant Accounting Policies [Line Items]
Premium revenue recognition period	12 months
Losses occurring
Significant Accounting Policies [Line Items]
Premium revenue recognition period	12 months
Risks attaching
Significant Accounting Policies [Line Items]
Premium revenue recognition period	24

-- None. No documentation exists for this element. --

No definition available.

Name:	acgl_PremiumRevenueRecognitionPeriod
Namespace Prefix:	acgl_
Data Type:	us-types:durationStringItemType
Balance Type:	na
Period Type:	duration